1 # SPDX-License-Identifier: GPL-2.0-only
6 default "/lib/modules/$(shell,uname -r)/.config"
7 default "/etc/kernel-config"
8 default "/boot/config-$(shell,uname -r)"
9 default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)"
11 config CC_VERSION_TEXT
13 default "$(CC_VERSION_TEXT)"
15 This is used in unclear ways:
17 - Re-run Kconfig when the compiler is updated
18 The 'default' property references the environment variable,
19 CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
20 When the compiler is updated, Kconfig will be invoked.
22 - Ensure full rebuild when the compier is updated
23 include/linux/kconfig.h contains this option in the comment line so
24 fixdep adds include/config/cc/version/text.h into the auto-generated
25 dependency. When the compiler is updated, syncconfig will touch it
26 and then every file will be rebuilt.
29 def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q gcc)
33 default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC
38 default $(shell,$(LD) --version | $(srctree)/scripts/ld-version.sh)
41 def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q clang)
44 def_bool $(success,$(LD) -v | head -n 1 | grep -q LLD)
48 default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
52 default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
56 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
57 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag))
59 config CC_CAN_LINK_STATIC
61 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT
62 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static)
64 config CC_HAS_ASM_GOTO
65 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
67 config CC_HAS_ASM_GOTO_OUTPUT
68 depends on CC_HAS_ASM_GOTO
69 def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
71 config TOOLS_SUPPORT_RELR
72 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
74 config CC_HAS_ASM_INLINE
75 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
84 config BUILDTIME_TABLE_SORT
87 config THREAD_INFO_IN_TASK
90 Select this to move thread_info off the stack into task_struct. To
91 make this work, an arch will need to remove all thread_info fields
92 except flags and fix any runtime bugs.
94 One subtle change that will be needed is to use try_get_task_stack()
95 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
104 depends on BROKEN || !SMP
107 config INIT_ENV_ARG_LIMIT
112 Maximum of each of the number of arguments and environment
113 variables passed to init from the kernel command line.
116 bool "Compile also drivers which will not load"
120 Some drivers can be compiled on a different platform than they are
121 intended to be run on. Despite they cannot be loaded there (or even
122 when they load they cannot be used due to missing HW support),
123 developers still, opposing to distributors, might want to build such
124 drivers to compile-test them.
126 If you are a developer and want to build everything available, say Y
127 here. If you are a user/distributor, say N here to exclude useless
128 drivers to be distributed.
130 config UAPI_HEADER_TEST
131 bool "Compile test UAPI headers"
132 depends on HEADERS_INSTALL && CC_CAN_LINK
134 Compile test headers exported to user-space to ensure they are
135 self-contained, i.e. compilable as standalone units.
137 If you are a developer or tester and want to ensure the exported
138 headers are self-contained, say Y here. Otherwise, choose N.
141 string "Local version - append to kernel release"
143 Append an extra string to the end of your kernel version.
144 This will show up when you type uname, for example.
145 The string you set here will be appended after the contents of
146 any files with a filename matching localversion* in your
147 object and source tree, in that order. Your total string can
148 be a maximum of 64 characters.
150 config LOCALVERSION_AUTO
151 bool "Automatically append version information to the version string"
153 depends on !COMPILE_TEST
155 This will try to automatically determine if the current tree is a
156 release tree by looking for git tags that belong to the current
157 top of tree revision.
159 A string of the format -gxxxxxxxx will be added to the localversion
160 if a git-based tree is found. The string generated by this will be
161 appended after any matching localversion* files, and after the value
162 set in CONFIG_LOCALVERSION.
164 (The actual string used here is the first eight characters produced
165 by running the command:
167 $ git rev-parse --verify HEAD
169 which is done within the script "scripts/setlocalversion".)
172 string "Build ID Salt"
175 The build ID is used to link binaries and their debug info. Setting
176 this option will use the value in the calculation of the build id.
177 This is mostly useful for distributions which want to ensure the
178 build is unique between builds. It's safe to leave the default.
180 config HAVE_KERNEL_GZIP
183 config HAVE_KERNEL_BZIP2
186 config HAVE_KERNEL_LZMA
189 config HAVE_KERNEL_XZ
192 config HAVE_KERNEL_LZO
195 config HAVE_KERNEL_LZ4
198 config HAVE_KERNEL_ZSTD
201 config HAVE_KERNEL_UNCOMPRESSED
205 prompt "Kernel compression mode"
207 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED
209 The linux kernel is a kind of self-extracting executable.
210 Several compression algorithms are available, which differ
211 in efficiency, compression and decompression speed.
212 Compression speed is only relevant when building a kernel.
213 Decompression speed is relevant at each boot.
215 If you have any problems with bzip2 or lzma compressed
216 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
217 version of this functionality (bzip2 only), for 2.4, was
218 supplied by Christian Ludwig)
220 High compression options are mostly useful for users, who
221 are low on disk space (embedded systems), but for whom ram
224 If in doubt, select 'gzip'
228 depends on HAVE_KERNEL_GZIP
230 The old and tried gzip compression. It provides a good balance
231 between compression ratio and decompression speed.
235 depends on HAVE_KERNEL_BZIP2
237 Its compression ratio and speed is intermediate.
238 Decompression speed is slowest among the choices. The kernel
239 size is about 10% smaller with bzip2, in comparison to gzip.
240 Bzip2 uses a large amount of memory. For modern kernels you
241 will need at least 8MB RAM or more for booting.
245 depends on HAVE_KERNEL_LZMA
247 This compression algorithm's ratio is best. Decompression speed
248 is between gzip and bzip2. Compression is slowest.
249 The kernel size is about 33% smaller with LZMA in comparison to gzip.
253 depends on HAVE_KERNEL_XZ
255 XZ uses the LZMA2 algorithm and instruction set specific
256 BCJ filters which can improve compression ratio of executable
257 code. The size of the kernel is about 30% smaller with XZ in
258 comparison to gzip. On architectures for which there is a BCJ
259 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
260 will create a few percent smaller kernel than plain LZMA.
262 The speed is about the same as with LZMA: The decompression
263 speed of XZ is better than that of bzip2 but worse than gzip
264 and LZO. Compression is slow.
268 depends on HAVE_KERNEL_LZO
270 Its compression ratio is the poorest among the choices. The kernel
271 size is about 10% bigger than gzip; however its speed
272 (both compression and decompression) is the fastest.
276 depends on HAVE_KERNEL_LZ4
278 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
279 A preliminary version of LZ4 de/compression tool is available at
280 <https://code.google.com/p/lz4/>.
282 Its compression ratio is worse than LZO. The size of the kernel
283 is about 8% bigger than LZO. But the decompression speed is
288 depends on HAVE_KERNEL_ZSTD
290 ZSTD is a compression algorithm targeting intermediate compression
291 with fast decompression speed. It will compress better than GZIP and
292 decompress around the same speed as LZO, but slower than LZ4. You
293 will need at least 192 KB RAM or more for booting. The zstd command
294 line tool is required for compression.
296 config KERNEL_UNCOMPRESSED
298 depends on HAVE_KERNEL_UNCOMPRESSED
300 Produce uncompressed kernel image. This option is usually not what
301 you want. It is useful for debugging the kernel in slow simulation
302 environments, where decompressing and moving the kernel is awfully
303 slow. This option allows early boot code to skip the decompressor
304 and jump right at uncompressed kernel image.
309 string "Default init path"
312 This option determines the default init for the system if no init=
313 option is passed on the kernel command line. If the requested path is
314 not present, we will still then move on to attempting further
315 locations (e.g. /sbin/init, etc). If this is empty, we will just use
316 the fallback list when init= is not passed.
318 config DEFAULT_HOSTNAME
319 string "Default hostname"
322 This option determines the default system hostname before userspace
323 calls sethostname(2). The kernel traditionally uses "(none)" here,
324 but you may wish to use a different default here to make a minimal
325 system more usable with less configuration.
328 # For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
329 # add proper SWAP support to them, in which case this can be remove.
335 bool "Support for paging of anonymous memory (swap)"
336 depends on MMU && BLOCK && !ARCH_NO_SWAP
339 This option allows you to choose whether you want to have support
340 for so called swap devices or swap files in your kernel that are
341 used to provide more virtual memory than the actual RAM present
342 in your computer. If unsure say Y.
347 Inter Process Communication is a suite of library functions and
348 system calls which let processes (running programs) synchronize and
349 exchange information. It is generally considered to be a good thing,
350 and some programs won't run unless you say Y here. In particular, if
351 you want to run the DOS emulator dosemu under Linux (read the
352 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
353 you'll need to say Y here.
355 You can find documentation about IPC with "info ipc" and also in
356 section 6.4 of the Linux Programmer's Guide, available from
357 <http://www.tldp.org/guides.html>.
359 config SYSVIPC_SYSCTL
366 bool "POSIX Message Queues"
369 POSIX variant of message queues is a part of IPC. In POSIX message
370 queues every message has a priority which decides about succession
371 of receiving it by a process. If you want to compile and run
372 programs written e.g. for Solaris with use of its POSIX message
373 queues (functions mq_*) say Y here.
375 POSIX message queues are visible as a filesystem called 'mqueue'
376 and can be mounted somewhere if you want to do filesystem
377 operations on message queues.
381 config POSIX_MQUEUE_SYSCTL
383 depends on POSIX_MQUEUE
388 bool "General notification queue"
392 This is a general notification queue for the kernel to pass events to
393 userspace by splicing them into pipes. It can be used in conjunction
394 with watches for key/keyring change notifications and device
397 See Documentation/watch_queue.rst
399 config CROSS_MEMORY_ATTACH
400 bool "Enable process_vm_readv/writev syscalls"
404 Enabling this option adds the system calls process_vm_readv and
405 process_vm_writev which allow a process with the correct privileges
406 to directly read from or write to another process' address space.
407 See the man page for more details.
410 bool "uselib syscall"
411 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
413 This option enables the uselib syscall, a system call used in the
414 dynamic linker from libc5 and earlier. glibc does not use this
415 system call. If you intend to run programs built on libc5 or
416 earlier, you may need to enable this syscall. Current systems
417 running glibc can safely disable this.
420 bool "Auditing support"
423 Enable auditing infrastructure that can be used with another
424 kernel subsystem, such as SELinux (which requires this for
425 logging of avc messages output). System call auditing is included
426 on architectures which support it.
428 config HAVE_ARCH_AUDITSYSCALL
433 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
436 source "kernel/irq/Kconfig"
437 source "kernel/time/Kconfig"
438 source "kernel/Kconfig.preempt"
440 menu "CPU/Task time and stats accounting"
442 config VIRT_CPU_ACCOUNTING
446 prompt "Cputime accounting"
447 default TICK_CPU_ACCOUNTING if !PPC64
448 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
450 # Kind of a stub config for the pure tick based cputime accounting
451 config TICK_CPU_ACCOUNTING
452 bool "Simple tick based cputime accounting"
453 depends on !S390 && !NO_HZ_FULL
455 This is the basic tick based cputime accounting that maintains
456 statistics about user, system and idle time spent on per jiffies
461 config VIRT_CPU_ACCOUNTING_NATIVE
462 bool "Deterministic task and CPU time accounting"
463 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
464 select VIRT_CPU_ACCOUNTING
466 Select this option to enable more accurate task and CPU time
467 accounting. This is done by reading a CPU counter on each
468 kernel entry and exit and on transitions within the kernel
469 between system, softirq and hardirq state, so there is a
470 small performance impact. In the case of s390 or IBM POWER > 5,
471 this also enables accounting of stolen time on logically-partitioned
474 config VIRT_CPU_ACCOUNTING_GEN
475 bool "Full dynticks CPU time accounting"
476 depends on HAVE_CONTEXT_TRACKING
477 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
478 depends on GENERIC_CLOCKEVENTS
479 select VIRT_CPU_ACCOUNTING
480 select CONTEXT_TRACKING
482 Select this option to enable task and CPU time accounting on full
483 dynticks systems. This accounting is implemented by watching every
484 kernel-user boundaries using the context tracking subsystem.
485 The accounting is thus performed at the expense of some significant
488 For now this is only useful if you are working on the full
489 dynticks subsystem development.
495 config IRQ_TIME_ACCOUNTING
496 bool "Fine granularity task level IRQ time accounting"
497 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
499 Select this option to enable fine granularity task irq time
500 accounting. This is done by reading a timestamp on each
501 transitions between softirq and hardirq state, so there can be a
502 small performance impact.
504 If in doubt, say N here.
506 config HAVE_SCHED_AVG_IRQ
508 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
511 config SCHED_THERMAL_PRESSURE
513 default y if ARM && ARM_CPU_TOPOLOGY
516 depends on CPU_FREQ_THERMAL
518 Select this option to enable thermal pressure accounting in the
519 scheduler. Thermal pressure is the value conveyed to the scheduler
520 that reflects the reduction in CPU compute capacity resulted from
521 thermal throttling. Thermal throttling occurs when the performance of
522 a CPU is capped due to high operating temperatures.
524 If selected, the scheduler will be able to balance tasks accordingly,
525 i.e. put less load on throttled CPUs than on non/less throttled ones.
527 This requires the architecture to implement
528 arch_set_thermal_pressure() and arch_get_thermal_pressure().
530 config BSD_PROCESS_ACCT
531 bool "BSD Process Accounting"
534 If you say Y here, a user level program will be able to instruct the
535 kernel (via a special system call) to write process accounting
536 information to a file: whenever a process exits, information about
537 that process will be appended to the file by the kernel. The
538 information includes things such as creation time, owning user,
539 command name, memory usage, controlling terminal etc. (the complete
540 list is in the struct acct in <file:include/linux/acct.h>). It is
541 up to the user level program to do useful things with this
542 information. This is generally a good idea, so say Y.
544 config BSD_PROCESS_ACCT_V3
545 bool "BSD Process Accounting version 3 file format"
546 depends on BSD_PROCESS_ACCT
549 If you say Y here, the process accounting information is written
550 in a new file format that also logs the process IDs of each
551 process and its parent. Note that this file format is incompatible
552 with previous v0/v1/v2 file formats, so you will need updated tools
553 for processing it. A preliminary version of these tools is available
554 at <http://www.gnu.org/software/acct/>.
557 bool "Export task/process statistics through netlink"
562 Export selected statistics for tasks/processes through the
563 generic netlink interface. Unlike BSD process accounting, the
564 statistics are available during the lifetime of tasks/processes as
565 responses to commands. Like BSD accounting, they are sent to user
570 config TASK_DELAY_ACCT
571 bool "Enable per-task delay accounting"
575 Collect information on time spent by a task waiting for system
576 resources like cpu, synchronous block I/O completion and swapping
577 in pages. Such statistics can help in setting a task's priorities
578 relative to other tasks for cpu, io, rss limits etc.
583 bool "Enable extended accounting over taskstats"
586 Collect extended task accounting data and send the data
587 to userland for processing over the taskstats interface.
591 config TASK_IO_ACCOUNTING
592 bool "Enable per-task storage I/O accounting"
593 depends on TASK_XACCT
595 Collect information on the number of bytes of storage I/O which this
601 bool "Pressure stall information tracking"
603 Collect metrics that indicate how overcommitted the CPU, memory,
604 and IO capacity are in the system.
606 If you say Y here, the kernel will create /proc/pressure/ with the
607 pressure statistics files cpu, memory, and io. These will indicate
608 the share of walltime in which some or all tasks in the system are
609 delayed due to contention of the respective resource.
611 In kernels with cgroup support, cgroups (cgroup2 only) will
612 have cpu.pressure, memory.pressure, and io.pressure files,
613 which aggregate pressure stalls for the grouped tasks only.
615 For more details see Documentation/accounting/psi.rst.
619 config PSI_DEFAULT_DISABLED
620 bool "Require boot parameter to enable pressure stall information tracking"
624 If set, pressure stall information tracking will be disabled
625 per default but can be enabled through passing psi=1 on the
626 kernel commandline during boot.
628 This feature adds some code to the task wakeup and sleep
629 paths of the scheduler. The overhead is too low to affect
630 common scheduling-intense workloads in practice (such as
631 webservers, memcache), but it does show up in artificial
632 scheduler stress tests, such as hackbench.
634 If you are paranoid and not sure what the kernel will be
639 endmenu # "CPU/Task time and stats accounting"
643 depends on SMP || COMPILE_TEST
646 Make sure that CPUs running critical tasks are not disturbed by
647 any source of "noise" such as unbound workqueues, timers, kthreads...
648 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
649 the "isolcpus=" boot parameter.
653 source "kernel/rcu/Kconfig"
660 tristate "Kernel .config support"
662 This option enables the complete Linux kernel ".config" file
663 contents to be saved in the kernel. It provides documentation
664 of which kernel options are used in a running kernel or in an
665 on-disk kernel. This information can be extracted from the kernel
666 image file with the script scripts/extract-ikconfig and used as
667 input to rebuild the current kernel or to build another kernel.
668 It can also be extracted from a running kernel by reading
669 /proc/config.gz if enabled (below).
672 bool "Enable access to .config through /proc/config.gz"
673 depends on IKCONFIG && PROC_FS
675 This option enables access to the kernel configuration file
676 through /proc/config.gz.
679 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
682 This option enables access to the in-kernel headers that are generated during
683 the build process. These can be used to build eBPF tracing programs,
684 or similar programs. If you build the headers as a module, a module called
685 kheaders.ko is built which can be loaded on-demand to get access to headers.
688 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
689 range 12 25 if !H8300
694 Select the minimal kernel log buffer size as a power of 2.
695 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
696 parameter, see below. Any higher size also might be forced
697 by "log_buf_len" boot parameter.
707 config LOG_CPU_MAX_BUF_SHIFT
708 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
711 default 12 if !BASE_SMALL
712 default 0 if BASE_SMALL
715 This option allows to increase the default ring buffer size
716 according to the number of CPUs. The value defines the contribution
717 of each CPU as a power of 2. The used space is typically only few
718 lines however it might be much more when problems are reported,
721 The increased size means that a new buffer has to be allocated and
722 the original static one is unused. It makes sense only on systems
723 with more CPUs. Therefore this value is used only when the sum of
724 contributions is greater than the half of the default kernel ring
725 buffer as defined by LOG_BUF_SHIFT. The default values are set
726 so that more than 16 CPUs are needed to trigger the allocation.
728 Also this option is ignored when "log_buf_len" kernel parameter is
729 used as it forces an exact (power of two) size of the ring buffer.
731 The number of possible CPUs is used for this computation ignoring
732 hotplugging making the computation optimal for the worst case
733 scenario while allowing a simple algorithm to be used from bootup.
735 Examples shift values and their meaning:
736 17 => 128 KB for each CPU
737 16 => 64 KB for each CPU
738 15 => 32 KB for each CPU
739 14 => 16 KB for each CPU
740 13 => 8 KB for each CPU
741 12 => 4 KB for each CPU
743 config PRINTK_SAFE_LOG_BUF_SHIFT
744 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
749 Select the size of an alternate printk per-CPU buffer where messages
750 printed from usafe contexts are temporary stored. One example would
751 be NMI messages, another one - printk recursion. The messages are
752 copied to the main log buffer in a safe context to avoid a deadlock.
753 The value defines the size as a power of 2.
755 Those messages are rare and limited. The largest one is when
756 a backtrace is printed. It usually fits into 4KB. Select
757 8KB if you want to be on the safe side.
760 17 => 128 KB for each CPU
761 16 => 64 KB for each CPU
762 15 => 32 KB for each CPU
763 14 => 16 KB for each CPU
764 13 => 8 KB for each CPU
765 12 => 4 KB for each CPU
768 # Architectures with an unreliable sched_clock() should select this:
770 config HAVE_UNSTABLE_SCHED_CLOCK
773 config GENERIC_SCHED_CLOCK
776 menu "Scheduler features"
779 bool "Enable utilization clamping for RT/FAIR tasks"
780 depends on CPU_FREQ_GOV_SCHEDUTIL
782 This feature enables the scheduler to track the clamped utilization
783 of each CPU based on RUNNABLE tasks scheduled on that CPU.
785 With this option, the user can specify the min and max CPU
786 utilization allowed for RUNNABLE tasks. The max utilization defines
787 the maximum frequency a task should use while the min utilization
788 defines the minimum frequency it should use.
790 Both min and max utilization clamp values are hints to the scheduler,
791 aiming at improving its frequency selection policy, but they do not
792 enforce or grant any specific bandwidth for tasks.
796 config UCLAMP_BUCKETS_COUNT
797 int "Number of supported utilization clamp buckets"
800 depends on UCLAMP_TASK
802 Defines the number of clamp buckets to use. The range of each bucket
803 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
804 number of clamp buckets the finer their granularity and the higher
805 the precision of clamping aggregation and tracking at run-time.
807 For example, with the minimum configuration value we will have 5
808 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
809 be refcounted in the [20..39]% bucket and will set the bucket clamp
810 effective value to 25%.
811 If a second 30% boosted task should be co-scheduled on the same CPU,
812 that task will be refcounted in the same bucket of the first task and
813 it will boost the bucket clamp effective value to 30%.
814 The clamp effective value of a bucket is reset to its nominal value
815 (20% in the example above) when there are no more tasks refcounted in
818 An additional boost/capping margin can be added to some tasks. In the
819 example above the 25% task will be boosted to 30% until it exits the
820 CPU. If that should be considered not acceptable on certain systems,
821 it's always possible to reduce the margin by increasing the number of
822 clamp buckets to trade off used memory for run-time tracking
825 If in doubt, use the default value.
830 # For architectures that want to enable the support for NUMA-affine scheduler
833 config ARCH_SUPPORTS_NUMA_BALANCING
837 # For architectures that prefer to flush all TLBs after a number of pages
838 # are unmapped instead of sending one IPI per page to flush. The architecture
839 # must provide guarantees on what happens if a clean TLB cache entry is
840 # written after the unmap. Details are in mm/rmap.c near the check for
841 # should_defer_flush. The architecture should also consider if the full flush
842 # and the refill costs are offset by the savings of sending fewer IPIs.
843 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
847 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
850 # For architectures that know their GCC __int128 support is sound
852 config ARCH_SUPPORTS_INT128
855 # For architectures that (ab)use NUMA to represent different memory regions
856 # all cpu-local but of different latencies, such as SuperH.
858 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
861 config NUMA_BALANCING
862 bool "Memory placement aware NUMA scheduler"
863 depends on ARCH_SUPPORTS_NUMA_BALANCING
864 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
865 depends on SMP && NUMA && MIGRATION
867 This option adds support for automatic NUMA aware memory/task placement.
868 The mechanism is quite primitive and is based on migrating memory when
869 it has references to the node the task is running on.
871 This system will be inactive on UMA systems.
873 config NUMA_BALANCING_DEFAULT_ENABLED
874 bool "Automatically enable NUMA aware memory/task placement"
876 depends on NUMA_BALANCING
878 If set, automatic NUMA balancing will be enabled if running on a NUMA
882 bool "Control Group support"
885 This option adds support for grouping sets of processes together, for
886 use with process control subsystems such as Cpusets, CFS, memory
887 controls or device isolation.
889 - Documentation/scheduler/sched-design-CFS.rst (CFS)
890 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
891 and resource control)
901 bool "Memory controller"
905 Provides control over the memory footprint of tasks in a cgroup.
909 depends on MEMCG && SWAP
914 depends on MEMCG && !SLOB
922 Generic block IO controller cgroup interface. This is the common
923 cgroup interface which should be used by various IO controlling
926 Currently, CFQ IO scheduler uses it to recognize task groups and
927 control disk bandwidth allocation (proportional time slice allocation)
928 to such task groups. It is also used by bio throttling logic in
929 block layer to implement upper limit in IO rates on a device.
931 This option only enables generic Block IO controller infrastructure.
932 One needs to also enable actual IO controlling logic/policy. For
933 enabling proportional weight division of disk bandwidth in CFQ, set
934 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
935 CONFIG_BLK_DEV_THROTTLING=y.
937 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
939 config CGROUP_WRITEBACK
941 depends on MEMCG && BLK_CGROUP
944 menuconfig CGROUP_SCHED
945 bool "CPU controller"
948 This feature lets CPU scheduler recognize task groups and control CPU
949 bandwidth allocation to such task groups. It uses cgroups to group
953 config FAIR_GROUP_SCHED
954 bool "Group scheduling for SCHED_OTHER"
955 depends on CGROUP_SCHED
959 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
960 depends on FAIR_GROUP_SCHED
963 This option allows users to define CPU bandwidth rates (limits) for
964 tasks running within the fair group scheduler. Groups with no limit
965 set are considered to be unconstrained and will run with no
967 See Documentation/scheduler/sched-bwc.rst for more information.
969 config RT_GROUP_SCHED
970 bool "Group scheduling for SCHED_RR/FIFO"
971 depends on CGROUP_SCHED
974 This feature lets you explicitly allocate real CPU bandwidth
975 to task groups. If enabled, it will also make it impossible to
976 schedule realtime tasks for non-root users until you allocate
977 realtime bandwidth for them.
978 See Documentation/scheduler/sched-rt-group.rst for more information.
982 config UCLAMP_TASK_GROUP
983 bool "Utilization clamping per group of tasks"
984 depends on CGROUP_SCHED
985 depends on UCLAMP_TASK
988 This feature enables the scheduler to track the clamped utilization
989 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
991 When this option is enabled, the user can specify a min and max
992 CPU bandwidth which is allowed for each single task in a group.
993 The max bandwidth allows to clamp the maximum frequency a task
994 can use, while the min bandwidth allows to define a minimum
995 frequency a task will always use.
997 When task group based utilization clamping is enabled, an eventually
998 specified task-specific clamp value is constrained by the cgroup
999 specified clamp value. Both minimum and maximum task clamping cannot
1000 be bigger than the corresponding clamping defined at task group level.
1005 bool "PIDs controller"
1007 Provides enforcement of process number limits in the scope of a
1008 cgroup. Any attempt to fork more processes than is allowed in the
1009 cgroup will fail. PIDs are fundamentally a global resource because it
1010 is fairly trivial to reach PID exhaustion before you reach even a
1011 conservative kmemcg limit. As a result, it is possible to grind a
1012 system to halt without being limited by other cgroup policies. The
1013 PIDs controller is designed to stop this from happening.
1015 It should be noted that organisational operations (such as attaching
1016 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
1017 since the PIDs limit only affects a process's ability to fork, not to
1021 bool "RDMA controller"
1023 Provides enforcement of RDMA resources defined by IB stack.
1024 It is fairly easy for consumers to exhaust RDMA resources, which
1025 can result into resource unavailability to other consumers.
1026 RDMA controller is designed to stop this from happening.
1027 Attaching processes with active RDMA resources to the cgroup
1028 hierarchy is allowed even if can cross the hierarchy's limit.
1030 config CGROUP_FREEZER
1031 bool "Freezer controller"
1033 Provides a way to freeze and unfreeze all tasks in a
1036 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1037 controller includes important in-kernel memory consumers per default.
1039 If you're using cgroup2, say N.
1041 config CGROUP_HUGETLB
1042 bool "HugeTLB controller"
1043 depends on HUGETLB_PAGE
1047 Provides a cgroup controller for HugeTLB pages.
1048 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1049 The limit is enforced during page fault. Since HugeTLB doesn't
1050 support page reclaim, enforcing the limit at page fault time implies
1051 that, the application will get SIGBUS signal if it tries to access
1052 HugeTLB pages beyond its limit. This requires the application to know
1053 beforehand how much HugeTLB pages it would require for its use. The
1054 control group is tracked in the third page lru pointer. This means
1055 that we cannot use the controller with huge page less than 3 pages.
1058 bool "Cpuset controller"
1061 This option will let you create and manage CPUSETs which
1062 allow dynamically partitioning a system into sets of CPUs and
1063 Memory Nodes and assigning tasks to run only within those sets.
1064 This is primarily useful on large SMP or NUMA systems.
1068 config PROC_PID_CPUSET
1069 bool "Include legacy /proc/<pid>/cpuset file"
1073 config CGROUP_DEVICE
1074 bool "Device controller"
1076 Provides a cgroup controller implementing whitelists for
1077 devices which a process in the cgroup can mknod or open.
1079 config CGROUP_CPUACCT
1080 bool "Simple CPU accounting controller"
1082 Provides a simple controller for monitoring the
1083 total CPU consumed by the tasks in a cgroup.
1086 bool "Perf controller"
1087 depends on PERF_EVENTS
1089 This option extends the perf per-cpu mode to restrict monitoring
1090 to threads which belong to the cgroup specified and run on the
1091 designated cpu. Or this can be used to have cgroup ID in samples
1092 so that it can monitor performance events among cgroups.
1097 bool "Support for eBPF programs attached to cgroups"
1098 depends on BPF_SYSCALL
1099 select SOCK_CGROUP_DATA
1101 Allow attaching eBPF programs to a cgroup using the bpf(2)
1102 syscall command BPF_PROG_ATTACH.
1104 In which context these programs are accessed depends on the type
1105 of attachment. For instance, programs that are attached using
1106 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1110 bool "Debug controller"
1112 depends on DEBUG_KERNEL
1114 This option enables a simple controller that exports
1115 debugging information about the cgroups framework. This
1116 controller is for control cgroup debugging only. Its
1117 interfaces are not stable.
1121 config SOCK_CGROUP_DATA
1127 menuconfig NAMESPACES
1128 bool "Namespaces support" if EXPERT
1129 depends on MULTIUSER
1132 Provides the way to make tasks work with different objects using
1133 the same id. For example same IPC id may refer to different objects
1134 or same user id or pid may refer to different tasks when used in
1135 different namespaces.
1140 bool "UTS namespace"
1143 In this namespace tasks see different info provided with the
1147 bool "TIME namespace"
1148 depends on GENERIC_VDSO_TIME_NS
1151 In this namespace boottime and monotonic clocks can be set.
1152 The time will keep going with the same pace.
1155 bool "IPC namespace"
1156 depends on (SYSVIPC || POSIX_MQUEUE)
1159 In this namespace tasks work with IPC ids which correspond to
1160 different IPC objects in different namespaces.
1163 bool "User namespace"
1166 This allows containers, i.e. vservers, to use user namespaces
1167 to provide different user info for different servers.
1169 When user namespaces are enabled in the kernel it is
1170 recommended that the MEMCG option also be enabled and that
1171 user-space use the memory control groups to limit the amount
1172 of memory a memory unprivileged users can use.
1177 bool "PID Namespaces"
1180 Support process id namespaces. This allows having multiple
1181 processes with the same pid as long as they are in different
1182 pid namespaces. This is a building block of containers.
1185 bool "Network namespace"
1189 Allow user space to create what appear to be multiple instances
1190 of the network stack.
1194 config CHECKPOINT_RESTORE
1195 bool "Checkpoint/restore support"
1196 select PROC_CHILDREN
1200 Enables additional kernel features in a sake of checkpoint/restore.
1201 In particular it adds auxiliary prctl codes to setup process text,
1202 data and heap segment sizes, and a few additional /proc filesystem
1205 If unsure, say N here.
1207 config SCHED_AUTOGROUP
1208 bool "Automatic process group scheduling"
1211 select FAIR_GROUP_SCHED
1213 This option optimizes the scheduler for common desktop workloads by
1214 automatically creating and populating task groups. This separation
1215 of workloads isolates aggressive CPU burners (like build jobs) from
1216 desktop applications. Task group autogeneration is currently based
1219 config SYSFS_DEPRECATED
1220 bool "Enable deprecated sysfs features to support old userspace tools"
1224 This option adds code that switches the layout of the "block" class
1225 devices, to not show up in /sys/class/block/, but only in
1228 This switch is only active when the sysfs.deprecated=1 boot option is
1229 passed or the SYSFS_DEPRECATED_V2 option is set.
1231 This option allows new kernels to run on old distributions and tools,
1232 which might get confused by /sys/class/block/. Since 2007/2008 all
1233 major distributions and tools handle this just fine.
1235 Recent distributions and userspace tools after 2009/2010 depend on
1236 the existence of /sys/class/block/, and will not work with this
1239 Only if you are using a new kernel on an old distribution, you might
1242 config SYSFS_DEPRECATED_V2
1243 bool "Enable deprecated sysfs features by default"
1246 depends on SYSFS_DEPRECATED
1248 Enable deprecated sysfs by default.
1250 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1253 Only if you are using a new kernel on an old distribution, you might
1254 need to say Y here. Even then, odds are you would not need it
1255 enabled, you can always pass the boot option if absolutely necessary.
1258 bool "Kernel->user space relay support (formerly relayfs)"
1261 This option enables support for relay interface support in
1262 certain file systems (such as debugfs).
1263 It is designed to provide an efficient mechanism for tools and
1264 facilities to relay large amounts of data from kernel space to
1269 config BLK_DEV_INITRD
1270 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1272 The initial RAM filesystem is a ramfs which is loaded by the
1273 boot loader (loadlin or lilo) and that is mounted as root
1274 before the normal boot procedure. It is typically used to
1275 load modules needed to mount the "real" root file system,
1276 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1278 If RAM disk support (BLK_DEV_RAM) is also included, this
1279 also enables initial RAM disk (initrd) support and adds
1280 15 Kbytes (more on some other architectures) to the kernel size.
1286 source "usr/Kconfig"
1291 bool "Boot config support"
1292 select BLK_DEV_INITRD
1294 Extra boot config allows system admin to pass a config file as
1295 complemental extension of kernel cmdline when booting.
1296 The boot config file must be attached at the end of initramfs
1297 with checksum, size and magic word.
1298 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1303 prompt "Compiler optimization level"
1304 default CC_OPTIMIZE_FOR_PERFORMANCE
1306 config CC_OPTIMIZE_FOR_PERFORMANCE
1307 bool "Optimize for performance (-O2)"
1309 This is the default optimization level for the kernel, building
1310 with the "-O2" compiler flag for best performance and most
1311 helpful compile-time warnings.
1313 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1314 bool "Optimize more for performance (-O3)"
1317 Choosing this option will pass "-O3" to your compiler to optimize
1318 the kernel yet more for performance.
1320 config CC_OPTIMIZE_FOR_SIZE
1321 bool "Optimize for size (-Os)"
1323 Choosing this option will pass "-Os" to your compiler resulting
1324 in a smaller kernel.
1328 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1331 This requires that the arch annotates or otherwise protects
1332 its external entry points from being discarded. Linker scripts
1333 must also merge .text.*, .data.*, and .bss.* correctly into
1334 output sections. Care must be taken not to pull in unrelated
1335 sections (e.g., '.text.init'). Typically '.' in section names
1336 is used to distinguish them from label names / C identifiers.
1338 config LD_DEAD_CODE_DATA_ELIMINATION
1339 bool "Dead code and data elimination (EXPERIMENTAL)"
1340 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1342 depends on $(cc-option,-ffunction-sections -fdata-sections)
1343 depends on $(ld-option,--gc-sections)
1345 Enable this if you want to do dead code and data elimination with
1346 the linker by compiling with -ffunction-sections -fdata-sections,
1347 and linking with --gc-sections.
1349 This can reduce on disk and in-memory size of the kernel
1350 code and static data, particularly for small configs and
1351 on small systems. This has the possibility of introducing
1352 silently broken kernel if the required annotations are not
1353 present. This option is not well tested yet, so use at your
1356 config LD_ORPHAN_WARN
1358 depends on ARCH_WANT_LD_ORPHAN_WARN
1359 depends on !LD_IS_LLD || LLD_VERSION >= 110000
1360 depends on $(ld-option,--orphan-handling=warn)
1368 config SYSCTL_EXCEPTION_TRACE
1371 Enable support for /proc/sys/debug/exception-trace.
1373 config SYSCTL_ARCH_UNALIGN_NO_WARN
1376 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1377 Allows arch to define/use @no_unaligned_warning to possibly warn
1378 about unaligned access emulation going on under the hood.
1380 config SYSCTL_ARCH_UNALIGN_ALLOW
1383 Enable support for /proc/sys/kernel/unaligned-trap
1384 Allows arches to define/use @unaligned_enabled to runtime toggle
1385 the unaligned access emulation.
1386 see arch/parisc/kernel/unaligned.c for reference
1388 config HAVE_PCSPKR_PLATFORM
1391 # interpreter that classic socket filters depend on
1396 bool "Configure standard kernel features (expert users)"
1397 # Unhide debug options, to make the on-by-default options visible
1400 This option allows certain base kernel options and settings
1401 to be disabled or tweaked. This is for specialized
1402 environments which can tolerate a "non-standard" kernel.
1403 Only use this if you really know what you are doing.
1406 bool "Enable 16-bit UID system calls" if EXPERT
1407 depends on HAVE_UID16 && MULTIUSER
1410 This enables the legacy 16-bit UID syscall wrappers.
1413 bool "Multiple users, groups and capabilities support" if EXPERT
1416 This option enables support for non-root users, groups and
1419 If you say N here, all processes will run with UID 0, GID 0, and all
1420 possible capabilities. Saying N here also compiles out support for
1421 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1424 If unsure, say Y here.
1426 config SGETMASK_SYSCALL
1427 bool "sgetmask/ssetmask syscalls support" if EXPERT
1428 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1430 sys_sgetmask and sys_ssetmask are obsolete system calls
1431 no longer supported in libc but still enabled by default in some
1434 If unsure, leave the default option here.
1436 config SYSFS_SYSCALL
1437 bool "Sysfs syscall support" if EXPERT
1440 sys_sysfs is an obsolete system call no longer supported in libc.
1441 Note that disabling this option is more secure but might break
1442 compatibility with some systems.
1444 If unsure say Y here.
1447 bool "open by fhandle syscalls" if EXPERT
1451 If you say Y here, a user level program will be able to map
1452 file names to handle and then later use the handle for
1453 different file system operations. This is useful in implementing
1454 userspace file servers, which now track files using handles instead
1455 of names. The handle would remain the same even if file names
1456 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1460 bool "Posix Clocks & timers" if EXPERT
1463 This includes native support for POSIX timers to the kernel.
1464 Some embedded systems have no use for them and therefore they
1465 can be configured out to reduce the size of the kernel image.
1467 When this option is disabled, the following syscalls won't be
1468 available: timer_create, timer_gettime: timer_getoverrun,
1469 timer_settime, timer_delete, clock_adjtime, getitimer,
1470 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1471 clock_getres and clock_nanosleep syscalls will be limited to
1472 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1478 bool "Enable support for printk" if EXPERT
1481 This option enables normal printk support. Removing it
1482 eliminates most of the message strings from the kernel image
1483 and makes the kernel more or less silent. As this makes it
1484 very difficult to diagnose system problems, saying N here is
1485 strongly discouraged.
1493 bool "BUG() support" if EXPERT
1496 Disabling this option eliminates support for BUG and WARN, reducing
1497 the size of your kernel image and potentially quietly ignoring
1498 numerous fatal conditions. You should only consider disabling this
1499 option for embedded systems with no facilities for reporting errors.
1505 bool "Enable ELF core dumps" if EXPERT
1507 Enable support for generating core dumps. Disabling saves about 4k.
1510 config PCSPKR_PLATFORM
1511 bool "Enable PC-Speaker support" if EXPERT
1512 depends on HAVE_PCSPKR_PLATFORM
1516 This option allows to disable the internal PC-Speaker
1517 support, saving some memory.
1521 bool "Enable full-sized data structures for core" if EXPERT
1523 Disabling this option reduces the size of miscellaneous core
1524 kernel data structures. This saves memory on small machines,
1525 but may reduce performance.
1528 bool "Enable futex support" if EXPERT
1532 Disabling this option will cause the kernel to be built without
1533 support for "fast userspace mutexes". The resulting kernel may not
1534 run glibc-based applications correctly.
1538 depends on FUTEX && RT_MUTEXES
1541 config HAVE_FUTEX_CMPXCHG
1545 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1546 is implemented and always working. This removes a couple of runtime
1550 bool "Enable eventpoll support" if EXPERT
1553 Disabling this option will cause the kernel to be built without
1554 support for epoll family of system calls.
1557 bool "Enable signalfd() system call" if EXPERT
1560 Enable the signalfd() system call that allows to receive signals
1561 on a file descriptor.
1566 bool "Enable timerfd() system call" if EXPERT
1569 Enable the timerfd() system call that allows to receive timer
1570 events on a file descriptor.
1575 bool "Enable eventfd() system call" if EXPERT
1578 Enable the eventfd() system call that allows to receive both
1579 kernel notification (ie. KAIO) or userspace notifications.
1584 bool "Use full shmem filesystem" if EXPERT
1588 The shmem is an internal filesystem used to manage shared memory.
1589 It is backed by swap and manages resource limits. It is also exported
1590 to userspace as tmpfs if TMPFS is enabled. Disabling this
1591 option replaces shmem and tmpfs with the much simpler ramfs code,
1592 which may be appropriate on small systems without swap.
1595 bool "Enable AIO support" if EXPERT
1598 This option enables POSIX asynchronous I/O which may by used
1599 by some high performance threaded applications. Disabling
1600 this option saves about 7k.
1603 bool "Enable IO uring support" if EXPERT
1607 This option enables support for the io_uring interface, enabling
1608 applications to submit and complete IO through submission and
1609 completion rings that are shared between the kernel and application.
1611 config ADVISE_SYSCALLS
1612 bool "Enable madvise/fadvise syscalls" if EXPERT
1615 This option enables the madvise and fadvise syscalls, used by
1616 applications to advise the kernel about their future memory or file
1617 usage, improving performance. If building an embedded system where no
1618 applications use these syscalls, you can disable this option to save
1621 config HAVE_ARCH_USERFAULTFD_WP
1624 Arch has userfaultfd write protection support
1627 bool "Enable membarrier() system call" if EXPERT
1630 Enable the membarrier() system call that allows issuing memory
1631 barriers across all running threads, which can be used to distribute
1632 the cost of user-space memory barriers asymmetrically by transforming
1633 pairs of memory barriers into pairs consisting of membarrier() and a
1639 bool "Load all symbols for debugging/ksymoops" if EXPERT
1642 Say Y here to let the kernel print out symbolic crash information and
1643 symbolic stack backtraces. This increases the size of the kernel
1644 somewhat, as all symbols have to be loaded into the kernel image.
1647 bool "Include all symbols in kallsyms"
1648 depends on DEBUG_KERNEL && KALLSYMS
1650 Normally kallsyms only contains the symbols of functions for nicer
1651 OOPS messages and backtraces (i.e., symbols from the text and inittext
1652 sections). This is sufficient for most cases. And only in very rare
1653 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1654 names of variables from the data sections, etc).
1656 This option makes sure that all symbols are loaded into the kernel
1657 image (i.e., symbols from all sections) in cost of increased kernel
1658 size (depending on the kernel configuration, it may be 300KiB or
1659 something like this).
1661 Say N unless you really need all symbols.
1663 config KALLSYMS_ABSOLUTE_PERCPU
1666 default X86_64 && SMP
1668 config KALLSYMS_BASE_RELATIVE
1673 Instead of emitting them as absolute values in the native word size,
1674 emit the symbol references in the kallsyms table as 32-bit entries,
1675 each containing a relative value in the range [base, base + U32_MAX]
1676 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1677 an absolute value in the range [0, S32_MAX] or a relative value in the
1678 range [base, base + S32_MAX], where base is the lowest relative symbol
1679 address encountered in the image.
1681 On 64-bit builds, this reduces the size of the address table by 50%,
1682 but more importantly, it results in entries whose values are build
1683 time constants, and no relocation pass is required at runtime to fix
1684 up the entries based on the runtime load address of the kernel.
1686 # end of the "standard kernel features (expert users)" menu
1688 # syscall, maps, verifier
1691 bool "LSM Instrumentation with BPF"
1692 depends on BPF_EVENTS
1693 depends on BPF_SYSCALL
1697 Enables instrumentation of the security hooks with eBPF programs for
1698 implementing dynamic MAC and Audit Policies.
1700 If you are unsure how to answer this question, answer N.
1703 bool "Enable bpf() system call"
1706 select TASKS_TRACE_RCU
1709 Enable the bpf() system call that allows to manipulate eBPF
1710 programs and maps via file descriptors.
1712 config ARCH_WANT_DEFAULT_BPF_JIT
1715 config BPF_JIT_ALWAYS_ON
1716 bool "Permanently enable BPF JIT and remove BPF interpreter"
1717 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
1719 Enables BPF JIT and removes BPF interpreter to avoid
1720 speculative execution of BPF instructions by the interpreter
1722 config BPF_JIT_DEFAULT_ON
1723 def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON
1724 depends on HAVE_EBPF_JIT && BPF_JIT
1726 source "kernel/bpf/preload/Kconfig"
1729 bool "Enable userfaultfd() system call"
1732 Enable the userfaultfd() system call that allows to intercept and
1733 handle page faults in userland.
1735 config ARCH_HAS_MEMBARRIER_CALLBACKS
1738 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1742 bool "Enable kcmp() system call" if EXPERT
1744 Enable the kernel resource comparison system call. It provides
1745 user-space with the ability to compare two processes to see if they
1746 share a common resource, such as a file descriptor or even virtual
1752 bool "Enable rseq() system call" if EXPERT
1754 depends on HAVE_RSEQ
1757 Enable the restartable sequences system call. It provides a
1758 user-space cache for the current CPU number value, which
1759 speeds up getting the current CPU number from user-space,
1760 as well as an ABI to speed up user-space operations on
1767 bool "Enabled debugging of rseq() system call" if EXPERT
1768 depends on RSEQ && DEBUG_KERNEL
1770 Enable extra debugging checks for the rseq system call.
1775 bool "Embedded system"
1776 option allnoconfig_y
1779 This option should be enabled if compiling the kernel for
1780 an embedded system so certain expert options are available
1783 config HAVE_PERF_EVENTS
1786 See tools/perf/design.txt for details.
1788 config PERF_USE_VMALLOC
1791 See tools/perf/design.txt for details
1794 bool "PC/104 support" if EXPERT
1796 Expose PC/104 form factor device drivers and options available for
1797 selection and configuration. Enable this option if your target
1798 machine has a PC/104 bus.
1800 menu "Kernel Performance Events And Counters"
1803 bool "Kernel performance events and counters"
1804 default y if PROFILING
1805 depends on HAVE_PERF_EVENTS
1809 Enable kernel support for various performance events provided
1810 by software and hardware.
1812 Software events are supported either built-in or via the
1813 use of generic tracepoints.
1815 Most modern CPUs support performance events via performance
1816 counter registers. These registers count the number of certain
1817 types of hw events: such as instructions executed, cachemisses
1818 suffered, or branches mis-predicted - without slowing down the
1819 kernel or applications. These registers can also trigger interrupts
1820 when a threshold number of events have passed - and can thus be
1821 used to profile the code that runs on that CPU.
1823 The Linux Performance Event subsystem provides an abstraction of
1824 these software and hardware event capabilities, available via a
1825 system call and used by the "perf" utility in tools/perf/. It
1826 provides per task and per CPU counters, and it provides event
1827 capabilities on top of those.
1831 config DEBUG_PERF_USE_VMALLOC
1833 bool "Debug: use vmalloc to back perf mmap() buffers"
1834 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1835 select PERF_USE_VMALLOC
1837 Use vmalloc memory to back perf mmap() buffers.
1839 Mostly useful for debugging the vmalloc code on platforms
1840 that don't require it.
1846 config VM_EVENT_COUNTERS
1848 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1850 VM event counters are needed for event counts to be shown.
1851 This option allows the disabling of the VM event counters
1852 on EXPERT systems. /proc/vmstat will only show page counts
1853 if VM event counters are disabled.
1857 bool "Enable SLUB debugging support" if EXPERT
1858 depends on SLUB && SYSFS
1860 SLUB has extensive debug support features. Disabling these can
1861 result in significant savings in code size. This also disables
1862 SLUB sysfs support. /sys/slab will not exist and there will be
1863 no support for cache validation etc.
1865 config SLUB_MEMCG_SYSFS_ON
1867 bool "Enable memcg SLUB sysfs support by default" if EXPERT
1868 depends on SLUB && SYSFS && MEMCG
1870 SLUB creates a directory under /sys/kernel/slab for each
1871 allocation cache to host info and debug files. If memory
1872 cgroup is enabled, each cache can have per memory cgroup
1873 caches. SLUB can create the same sysfs directories for these
1874 caches under /sys/kernel/slab/CACHE/cgroup but it can lead
1875 to a very high number of debug files being created. This is
1876 controlled by slub_memcg_sysfs boot parameter and this
1877 config option determines the parameter's default value.
1880 bool "Disable heap randomization"
1883 Randomizing heap placement makes heap exploits harder, but it
1884 also breaks ancient binaries (including anything libc5 based).
1885 This option changes the bootup default to heap randomization
1886 disabled, and can be overridden at runtime by setting
1887 /proc/sys/kernel/randomize_va_space to 2.
1889 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1892 prompt "Choose SLAB allocator"
1895 This option allows to select a slab allocator.
1899 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1901 The regular slab allocator that is established and known to work
1902 well in all environments. It organizes cache hot objects in
1903 per cpu and per node queues.
1906 bool "SLUB (Unqueued Allocator)"
1907 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1909 SLUB is a slab allocator that minimizes cache line usage
1910 instead of managing queues of cached objects (SLAB approach).
1911 Per cpu caching is realized using slabs of objects instead
1912 of queues of objects. SLUB can use memory efficiently
1913 and has enhanced diagnostics. SLUB is the default choice for
1918 bool "SLOB (Simple Allocator)"
1920 SLOB replaces the stock allocator with a drastically simpler
1921 allocator. SLOB is generally more space efficient but
1922 does not perform as well on large systems.
1926 config SLAB_MERGE_DEFAULT
1927 bool "Allow slab caches to be merged"
1930 For reduced kernel memory fragmentation, slab caches can be
1931 merged when they share the same size and other characteristics.
1932 This carries a risk of kernel heap overflows being able to
1933 overwrite objects from merged caches (and more easily control
1934 cache layout), which makes such heap attacks easier to exploit
1935 by attackers. By keeping caches unmerged, these kinds of exploits
1936 can usually only damage objects in the same cache. To disable
1937 merging at runtime, "slab_nomerge" can be passed on the kernel
1940 config SLAB_FREELIST_RANDOM
1941 bool "Randomize slab freelist"
1942 depends on SLAB || SLUB
1944 Randomizes the freelist order used on creating new pages. This
1945 security feature reduces the predictability of the kernel slab
1946 allocator against heap overflows.
1948 config SLAB_FREELIST_HARDENED
1949 bool "Harden slab freelist metadata"
1950 depends on SLAB || SLUB
1952 Many kernel heap attacks try to target slab cache metadata and
1953 other infrastructure. This options makes minor performance
1954 sacrifices to harden the kernel slab allocator against common
1955 freelist exploit methods. Some slab implementations have more
1956 sanity-checking than others. This option is most effective with
1959 config SHUFFLE_PAGE_ALLOCATOR
1960 bool "Page allocator randomization"
1961 default SLAB_FREELIST_RANDOM && ACPI_NUMA
1963 Randomization of the page allocator improves the average
1964 utilization of a direct-mapped memory-side-cache. See section
1965 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
1966 6.2a specification for an example of how a platform advertises
1967 the presence of a memory-side-cache. There are also incidental
1968 security benefits as it reduces the predictability of page
1969 allocations to compliment SLAB_FREELIST_RANDOM, but the
1970 default granularity of shuffling on the "MAX_ORDER - 1" i.e,
1971 10th order of pages is selected based on cache utilization
1974 While the randomization improves cache utilization it may
1975 negatively impact workloads on platforms without a cache. For
1976 this reason, by default, the randomization is enabled only
1977 after runtime detection of a direct-mapped memory-side-cache.
1978 Otherwise, the randomization may be force enabled with the
1979 'page_alloc.shuffle' kernel command line parameter.
1983 config SLUB_CPU_PARTIAL
1985 depends on SLUB && SMP
1986 bool "SLUB per cpu partial cache"
1988 Per cpu partial caches accelerate objects allocation and freeing
1989 that is local to a processor at the price of more indeterminism
1990 in the latency of the free. On overflow these caches will be cleared
1991 which requires the taking of locks that may cause latency spikes.
1992 Typically one would choose no for a realtime system.
1994 config MMAP_ALLOW_UNINITIALIZED
1995 bool "Allow mmapped anonymous memory to be uninitialized"
1996 depends on EXPERT && !MMU
1999 Normally, and according to the Linux spec, anonymous memory obtained
2000 from mmap() has its contents cleared before it is passed to
2001 userspace. Enabling this config option allows you to request that
2002 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
2003 providing a huge performance boost. If this option is not enabled,
2004 then the flag will be ignored.
2006 This is taken advantage of by uClibc's malloc(), and also by
2007 ELF-FDPIC binfmt's brk and stack allocator.
2009 Because of the obvious security issues, this option should only be
2010 enabled on embedded devices where you control what is run in
2011 userspace. Since that isn't generally a problem on no-MMU systems,
2012 it is normally safe to say Y here.
2014 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
2016 config SYSTEM_DATA_VERIFICATION
2018 select SYSTEM_TRUSTED_KEYRING
2022 select ASYMMETRIC_KEY_TYPE
2023 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
2026 select X509_CERTIFICATE_PARSER
2027 select PKCS7_MESSAGE_PARSER
2029 Provide PKCS#7 message verification using the contents of the system
2030 trusted keyring to provide public keys. This then can be used for
2031 module verification, kexec image verification and firmware blob
2035 bool "Profiling support"
2037 Say Y here to enable the extended profiling support mechanisms used
2038 by profilers such as OProfile.
2041 # Place an empty function call at each tracepoint site. Can be
2042 # dynamically changed for a probe function.
2047 endmenu # General setup
2049 source "arch/Kconfig"
2056 default 0 if BASE_FULL
2057 default 1 if !BASE_FULL
2059 config MODULE_SIG_FORMAT
2061 select SYSTEM_DATA_VERIFICATION
2064 bool "Enable loadable module support"
2067 Kernel modules are small pieces of compiled code which can
2068 be inserted in the running kernel, rather than being
2069 permanently built into the kernel. You use the "modprobe"
2070 tool to add (and sometimes remove) them. If you say Y here,
2071 many parts of the kernel can be built as modules (by
2072 answering M instead of Y where indicated): this is most
2073 useful for infrequently used options which are not required
2074 for booting. For more information, see the man pages for
2075 modprobe, lsmod, modinfo, insmod and rmmod.
2077 If you say Y here, you will need to run "make
2078 modules_install" to put the modules under /lib/modules/
2079 where modprobe can find them (you may need to be root to do
2086 config MODULE_FORCE_LOAD
2087 bool "Forced module loading"
2090 Allow loading of modules without version information (ie. modprobe
2091 --force). Forced module loading sets the 'F' (forced) taint flag and
2092 is usually a really bad idea.
2094 config MODULE_UNLOAD
2095 bool "Module unloading"
2097 Without this option you will not be able to unload any
2098 modules (note that some modules may not be unloadable
2099 anyway), which makes your kernel smaller, faster
2100 and simpler. If unsure, say Y.
2102 config MODULE_FORCE_UNLOAD
2103 bool "Forced module unloading"
2104 depends on MODULE_UNLOAD
2106 This option allows you to force a module to unload, even if the
2107 kernel believes it is unsafe: the kernel will remove the module
2108 without waiting for anyone to stop using it (using the -f option to
2109 rmmod). This is mainly for kernel developers and desperate users.
2113 bool "Module versioning support"
2115 Usually, you have to use modules compiled with your kernel.
2116 Saying Y here makes it sometimes possible to use modules
2117 compiled for different kernels, by adding enough information
2118 to the modules to (hopefully) spot any changes which would
2119 make them incompatible with the kernel you are running. If
2122 config ASM_MODVERSIONS
2124 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2126 This enables module versioning for exported symbols also from
2127 assembly. This can be enabled only when the target architecture
2130 config MODULE_REL_CRCS
2132 depends on MODVERSIONS
2134 config MODULE_SRCVERSION_ALL
2135 bool "Source checksum for all modules"
2137 Modules which contain a MODULE_VERSION get an extra "srcversion"
2138 field inserted into their modinfo section, which contains a
2139 sum of the source files which made it. This helps maintainers
2140 see exactly which source was used to build a module (since
2141 others sometimes change the module source without updating
2142 the version). With this option, such a "srcversion" field
2143 will be created for all modules. If unsure, say N.
2146 bool "Module signature verification"
2147 select MODULE_SIG_FORMAT
2149 Check modules for valid signatures upon load: the signature
2150 is simply appended to the module. For more information see
2151 <file:Documentation/admin-guide/module-signing.rst>.
2153 Note that this option adds the OpenSSL development packages as a
2154 kernel build dependency so that the signing tool can use its crypto
2157 You should enable this option if you wish to use either
2158 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2159 another LSM - otherwise unsigned modules will be loadable regardless
2160 of the lockdown policy.
2162 !!!WARNING!!! If you enable this option, you MUST make sure that the
2163 module DOES NOT get stripped after being signed. This includes the
2164 debuginfo strip done by some packagers (such as rpmbuild) and
2165 inclusion into an initramfs that wants the module size reduced.
2167 config MODULE_SIG_FORCE
2168 bool "Require modules to be validly signed"
2169 depends on MODULE_SIG
2171 Reject unsigned modules or signed modules for which we don't have a
2172 key. Without this, such modules will simply taint the kernel.
2174 config MODULE_SIG_ALL
2175 bool "Automatically sign all modules"
2177 depends on MODULE_SIG
2179 Sign all modules during make modules_install. Without this option,
2180 modules must be signed manually, using the scripts/sign-file tool.
2182 comment "Do not forget to sign required modules with scripts/sign-file"
2183 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2186 prompt "Which hash algorithm should modules be signed with?"
2187 depends on MODULE_SIG
2189 This determines which sort of hashing algorithm will be used during
2190 signature generation. This algorithm _must_ be built into the kernel
2191 directly so that signature verification can take place. It is not
2192 possible to load a signed module containing the algorithm to check
2193 the signature on that module.
2195 config MODULE_SIG_SHA1
2196 bool "Sign modules with SHA-1"
2199 config MODULE_SIG_SHA224
2200 bool "Sign modules with SHA-224"
2201 select CRYPTO_SHA256
2203 config MODULE_SIG_SHA256
2204 bool "Sign modules with SHA-256"
2205 select CRYPTO_SHA256
2207 config MODULE_SIG_SHA384
2208 bool "Sign modules with SHA-384"
2209 select CRYPTO_SHA512
2211 config MODULE_SIG_SHA512
2212 bool "Sign modules with SHA-512"
2213 select CRYPTO_SHA512
2217 config MODULE_SIG_HASH
2219 depends on MODULE_SIG
2220 default "sha1" if MODULE_SIG_SHA1
2221 default "sha224" if MODULE_SIG_SHA224
2222 default "sha256" if MODULE_SIG_SHA256
2223 default "sha384" if MODULE_SIG_SHA384
2224 default "sha512" if MODULE_SIG_SHA512
2226 config MODULE_COMPRESS
2227 bool "Compress modules on installation"
2230 Compresses kernel modules when 'make modules_install' is run; gzip or
2231 xz depending on "Compression algorithm" below.
2233 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2235 Out-of-tree kernel modules installed using Kbuild will also be
2236 compressed upon installation.
2238 Note: for modules inside an initrd or initramfs, it's more efficient
2239 to compress the whole initrd or initramfs instead.
2241 Note: This is fully compatible with signed modules.
2246 prompt "Compression algorithm"
2247 depends on MODULE_COMPRESS
2248 default MODULE_COMPRESS_GZIP
2250 This determines which sort of compression will be used during
2251 'make modules_install'.
2253 GZIP (default) and XZ are supported.
2255 config MODULE_COMPRESS_GZIP
2258 config MODULE_COMPRESS_XZ
2263 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2264 bool "Allow loading of modules with missing namespace imports"
2266 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2267 a namespace. A module that makes use of a symbol exported with such a
2268 namespace is required to import the namespace via MODULE_IMPORT_NS().
2269 There is no technical reason to enforce correct namespace imports,
2270 but it creates consistency between symbols defining namespaces and
2271 users importing namespaces they make use of. This option relaxes this
2272 requirement and lifts the enforcement when loading a module.
2276 config UNUSED_SYMBOLS
2277 bool "Enable unused/obsolete exported symbols"
2280 Unused but exported symbols make the kernel needlessly bigger. For
2281 that reason most of these unused exports will soon be removed. This
2282 option is provided temporarily to provide a transition period in case
2283 some external kernel module needs one of these symbols anyway. If you
2284 encounter such a case in your module, consider if you are actually
2285 using the right API. (rationale: since nobody in the kernel is using
2286 this in a module, there is a pretty good chance it's actually the
2287 wrong interface to use). If you really need the symbol, please send a
2288 mail to the linux kernel mailing list mentioning the symbol and why
2289 you really need it, and what the merge plan to the mainline kernel for
2292 config TRIM_UNUSED_KSYMS
2293 bool "Trim unused exported kernel symbols"
2294 depends on !UNUSED_SYMBOLS
2296 The kernel and some modules make many symbols available for
2297 other modules to use via EXPORT_SYMBOL() and variants. Depending
2298 on the set of modules being selected in your kernel configuration,
2299 many of those exported symbols might never be used.
2301 This option allows for unused exported symbols to be dropped from
2302 the build. In turn, this provides the compiler more opportunities
2303 (especially when using LTO) for optimizing the code and reducing
2304 binary size. This might have some security advantages as well.
2306 If unsure, or if you need to build out-of-tree modules, say N.
2308 config UNUSED_KSYMS_WHITELIST
2309 string "Whitelist of symbols to keep in ksymtab"
2310 depends on TRIM_UNUSED_KSYMS
2312 By default, all unused exported symbols will be un-exported from the
2313 build when TRIM_UNUSED_KSYMS is selected.
2315 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
2316 exported at all times, even in absence of in-tree users. The value to
2317 set here is the path to a text file containing the list of symbols,
2318 one per line. The path can be absolute, or relative to the kernel
2323 config MODULES_TREE_LOOKUP
2325 depends on PERF_EVENTS || TRACING
2327 config INIT_ALL_POSSIBLE
2330 Back when each arch used to define their own cpu_online_mask and
2331 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2332 with all 1s, and others with all 0s. When they were centralised,
2333 it was better to provide this option than to break all the archs
2334 and have several arch maintainers pursuing me down dark alleys.
2336 source "block/Kconfig"
2338 config PREEMPT_NOTIFIERS
2348 Build a simple ASN.1 grammar compiler that produces a bytecode output
2349 that can be interpreted by the ASN.1 stream decoder and used to
2350 inform it as to what tags are to be expected in a stream and what
2351 functions to call on what tags.
2353 source "kernel/Kconfig.locks"
2355 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
2358 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2361 # It may be useful for an architecture to override the definitions of the
2362 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2363 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2364 # different calling convention for syscalls. They can also override the
2365 # macros for not-implemented syscalls in kernel/sys_ni.c and
2366 # kernel/time/posix-stubs.c. All these overrides need to be available in
2367 # <asm/syscall_wrapper.h>.
2368 config ARCH_HAS_SYSCALL_WRAPPER
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