disable
Do not enable intel_pstate as the default
scaling driver for the supported processors
+ active
+ Use intel_pstate driver to bypass the scaling
+ governors layer of cpufreq and provides it own
+ algorithms for p-state selection. There are two
+ P-state selection algorithms provided by
+ intel_pstate in the active mode: powersave and
+ performance. The way they both operate depends
+ on whether or not the hardware managed P-states
+ (HWP) feature has been enabled in the processor
+ and possibly on the processor model.
passive
Use intel_pstate as a scaling driver, but configure it
to work with generic cpufreq governors (instead of
If the value is 0 (the default), KVM will pick a period based
on the ratio, such that a page is zapped after 1 hour on average.
- kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
- Default is 1 (enabled)
+ kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
+ KVM/SVM. Default is 1 (enabled).
- kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
- for all guests.
- Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
+ kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
+ a.k.a. Two-Dimensional Page Tables. Default is 1
+ (enabled). Disable by KVM if hardware lacks support
+ for NPT.
kvm-arm.mode=
[KVM,ARM] Select one of KVM/arm64's modes of operation.
Format: <integer>
Default: 5
- kvm-intel.ept= [KVM,Intel] Disable extended page tables
- (virtualized MMU) support on capable Intel chips.
- Default is 1 (enabled)
+ kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
+ a.k.a. Two-Dimensional Page Tables. Default is 1
+ (enabled). Disable by KVM if hardware lacks support
+ for EPT.
kvm-intel.emulate_invalid_guest_state=
- [KVM,Intel] Disable emulation of invalid guest state.
- Ignored if kvm-intel.enable_unrestricted_guest=1, as
- guest state is never invalid for unrestricted guests.
- This param doesn't apply to nested guests (L2), as KVM
- never emulates invalid L2 guest state.
- Default is 1 (enabled)
+ [KVM,Intel] Control whether to emulate invalid guest
+ state. Ignored if kvm-intel.enable_unrestricted_guest=1,
+ as guest state is never invalid for unrestricted
+ guests. This param doesn't apply to nested guests (L2),
+ as KVM never emulates invalid L2 guest state.
+ Default is 1 (enabled).
kvm-intel.flexpriority=
- [KVM,Intel] Disable FlexPriority feature (TPR shadow).
- Default is 1 (enabled)
+ [KVM,Intel] Control KVM's use of FlexPriority feature
+ (TPR shadow). Default is 1 (enabled). Disalbe by KVM if
+ hardware lacks support for it.
kvm-intel.nested=
- [KVM,Intel] Enable VMX nesting (nVMX).
- Default is 0 (disabled)
+ [KVM,Intel] Control nested virtualization feature in
+ KVM/VMX. Default is 1 (enabled).
kvm-intel.unrestricted_guest=
- [KVM,Intel] Disable unrestricted guest feature
- (virtualized real and unpaged mode) on capable
- Intel chips. Default is 1 (enabled)
+ [KVM,Intel] Control KVM's use of unrestricted guest
+ feature (virtualized real and unpaged mode). Default
+ is 1 (enabled). Disable by KVM if EPT is disabled or
+ hardware lacks support for it.
kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
CVE-2018-3620.
Default is cond (do L1 cache flush in specific instances)
- kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
- feature (tagged TLBs) on capable Intel chips.
- Default is 1 (enabled)
+ kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
+ Identification feature (tagged TLBs). Default is 1
+ (enabled). Disable by KVM if hardware lacks support
+ for it.
l1d_flush= [X86,INTEL]
Control mitigation for L1D based snooping vulnerability.
"__percpu",
"__rcu",
"__user",
+ "__force",
# include/linux/compiler_attributes.h:
"__alias",
.. kernel-doc:: lib/cmdline.c
:export:
+Error Pointers
+--------------
+
+.. kernel-doc:: include/linux/err.h
+ :internal:
+
Sorting
-------
::
struct dma_async_tx_descriptor *
- async_<operation>(<op specific parameters>, struct async_submit ctl *submit)
+ async_<operation>(<op specific parameters>, struct async_submit_ctl *submit)
3.2 Supported operations
------------------------
function name exists. If you see ``c:func:`` use in a kernel document,
please feel free to remove it.
+Tables
+------
+
+ReStructuredText provides several options for table syntax. Kernel style for
+tables is to prefer *simple table* syntax or *grid table* syntax. See the
+`reStructuredText user reference for table syntax`_ for more details.
+
+.. _reStructuredText user reference for table syntax:
+ https://docutils.sourceforge.io/docs/user/rst/quickref.html#tables
list tables
------------
+~~~~~~~~~~~
The list-table formats can be useful for tables that are not easily laid
out in the usual Sphinx ASCII-art formats. These formats are nearly
$ cat >.git/hooks/applypatch-msg <<'EOF'
#!/bin/sh
. git-sh-setup
- perl -pi -e 's|^Message-Id:\s*<?([^>]+)>?$|Link: https://lore.kernel.org/r/$1|g;' "$1"
+ perl -pi -e 's|^Message-I[dD]:\s*<?([^>]+)>?$|Link: https://lore.kernel.org/r/$1|g;' "$1"
test -x "$GIT_DIR/hooks/commit-msg" &&
exec "$GIT_DIR/hooks/commit-msg" ${1+"$@"}
:
===========
Page Tables
===========
+
+Paged virtual memory was invented along with virtual memory as a concept in
+1962 on the Ferranti Atlas Computer which was the first computer with paged
+virtual memory. The feature migrated to newer computers and became a de facto
+feature of all Unix-like systems as time went by. In 1985 the feature was
+included in the Intel 80386, which was the CPU Linux 1.0 was developed on.
+
+Page tables map virtual addresses as seen by the CPU into physical addresses
+as seen on the external memory bus.
+
+Linux defines page tables as a hierarchy which is currently five levels in
+height. The architecture code for each supported architecture will then
+map this to the restrictions of the hardware.
+
+The physical address corresponding to the virtual address is often referenced
+by the underlying physical page frame. The **page frame number** or **pfn**
+is the physical address of the page (as seen on the external memory bus)
+divided by `PAGE_SIZE`.
+
+Physical memory address 0 will be *pfn 0* and the highest pfn will be
+the last page of physical memory the external address bus of the CPU can
+address.
+
+With a page granularity of 4KB and a address range of 32 bits, pfn 0 is at
+address 0x00000000, pfn 1 is at address 0x00001000, pfn 2 is at 0x00002000
+and so on until we reach pfn 0xfffff at 0xfffff000. With 16KB pages pfs are
+at 0x00004000, 0x00008000 ... 0xffffc000 and pfn goes from 0 to 0x3fffff.
+
+As you can see, with 4KB pages the page base address uses bits 12-31 of the
+address, and this is why `PAGE_SHIFT` in this case is defined as 12 and
+`PAGE_SIZE` is usually defined in terms of the page shift as `(1 << PAGE_SHIFT)`
+
+Over time a deeper hierarchy has been developed in response to increasing memory
+sizes. When Linux was created, 4KB pages and a single page table called
+`swapper_pg_dir` with 1024 entries was used, covering 4MB which coincided with
+the fact that Torvald's first computer had 4MB of physical memory. Entries in
+this single table were referred to as *PTE*:s - page table entries.
+
+The software page table hierarchy reflects the fact that page table hardware has
+become hierarchical and that in turn is done to save page table memory and
+speed up mapping.
+
+One could of course imagine a single, linear page table with enormous amounts
+of entries, breaking down the whole memory into single pages. Such a page table
+would be very sparse, because large portions of the virtual memory usually
+remains unused. By using hierarchical page tables large holes in the virtual
+address space does not waste valuable page table memory, because it will suffice
+to mark large areas as unmapped at a higher level in the page table hierarchy.
+
+Additionally, on modern CPUs, a higher level page table entry can point directly
+to a physical memory range, which allows mapping a contiguous range of several
+megabytes or even gigabytes in a single high-level page table entry, taking
+shortcuts in mapping virtual memory to physical memory: there is no need to
+traverse deeper in the hierarchy when you find a large mapped range like this.
+
+The page table hierarchy has now developed into this::
+
+ +-----+
+ | PGD |
+ +-----+
+ |
+ | +-----+
+ +-->| P4D |
+ +-----+
+ |
+ | +-----+
+ +-->| PUD |
+ +-----+
+ |
+ | +-----+
+ +-->| PMD |
+ +-----+
+ |
+ | +-----+
+ +-->| PTE |
+ +-----+
+
+
+Symbols on the different levels of the page table hierarchy have the following
+meaning beginning from the bottom:
+
+- **pte**, `pte_t`, `pteval_t` = **Page Table Entry** - mentioned earlier.
+ The *pte* is an array of `PTRS_PER_PTE` elements of the `pteval_t` type, each
+ mapping a single page of virtual memory to a single page of physical memory.
+ The architecture defines the size and contents of `pteval_t`.
+
+ A typical example is that the `pteval_t` is a 32- or 64-bit value with the
+ upper bits being a **pfn** (page frame number), and the lower bits being some
+ architecture-specific bits such as memory protection.
+
+ The **entry** part of the name is a bit confusing because while in Linux 1.0
+ this did refer to a single page table entry in the single top level page
+ table, it was retrofitted to be an array of mapping elements when two-level
+ page tables were first introduced, so the *pte* is the lowermost page
+ *table*, not a page table *entry*.
+
+- **pmd**, `pmd_t`, `pmdval_t` = **Page Middle Directory**, the hierarchy right
+ above the *pte*, with `PTRS_PER_PMD` references to the *pte*:s.
+
+- **pud**, `pud_t`, `pudval_t` = **Page Upper Directory** was introduced after
+ the other levels to handle 4-level page tables. It is potentially unused,
+ or *folded* as we will discuss later.
+
+- **p4d**, `p4d_t`, `p4dval_t` = **Page Level 4 Directory** was introduced to
+ handle 5-level page tables after the *pud* was introduced. Now it was clear
+ that we needed to replace *pgd*, *pmd*, *pud* etc with a figure indicating the
+ directory level and that we cannot go on with ad hoc names any more. This
+ is only used on systems which actually have 5 levels of page tables, otherwise
+ it is folded.
+
+- **pgd**, `pgd_t`, `pgdval_t` = **Page Global Directory** - the Linux kernel
+ main page table handling the PGD for the kernel memory is still found in
+ `swapper_pg_dir`, but each userspace process in the system also has its own
+ memory context and thus its own *pgd*, found in `struct mm_struct` which
+ in turn is referenced to in each `struct task_struct`. So tasks have memory
+ context in the form of a `struct mm_struct` and this in turn has a
+ `struct pgt_t *pgd` pointer to the corresponding page global directory.
+
+To repeat: each level in the page table hierarchy is a *array of pointers*, so
+the **pgd** contains `PTRS_PER_PGD` pointers to the next level below, **p4d**
+contains `PTRS_PER_P4D` pointers to **pud** items and so on. The number of
+pointers on each level is architecture-defined.::
+
+ PMD
+ --> +-----+ PTE
+ | ptr |-------> +-----+
+ | ptr |- | ptr |-------> PAGE
+ | ptr | \ | ptr |
+ | ptr | \ ...
+ | ... | \
+ | ptr | \ PTE
+ +-----+ +----> +-----+
+ | ptr |-------> PAGE
+ | ptr |
+ ...
+
+
+Page Table Folding
+==================
+
+If the architecture does not use all the page table levels, they can be *folded*
+which means skipped, and all operations performed on page tables will be
+compile-time augmented to just skip a level when accessing the next lower
+level.
+
+Page table handling code that wishes to be architecture-neutral, such as the
+virtual memory manager, will need to be written so that it traverses all of the
+currently five levels. This style should also be preferred for
+architecture-specific code, so as to be robust to future changes.
questions. Some developers can get impatient with people who clearly
have not done their homework.
-- Avoid top-posting (the practice of putting your answer above the quoted
- text you are responding to). It makes your response harder to read and
- makes a poor impression.
+- Use interleaved ("inline") replies, which makes your response easier to
+ read. (i.e. avoid top-posting -- the practice of putting your answer above
+ the quoted text you are responding to.) For more details, see
+ :ref:`Documentation/process/submitting-patches.rst <interleaved_replies>`.
- Ask on the correct mailing list. Linux-kernel may be the general meeting
point, but it is not the best place to find developers from all
these tools is regzbot, which heavily relies on the "Link:" tags to associate
reports for regression with changes resolving them.
-Prioritize work on fixing regressions
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-You should fix any reported regression as quickly as possible, to provide
-affected users with a solution in a timely manner and prevent more users from
-running into the issue; nevertheless developers need to take enough time and
-care to ensure regression fixes do not cause additional damage.
-
-In the end though, developers should give their best to prevent users from
-running into situations where a regression leaves them only three options: "run
-a kernel with a regression that seriously impacts usage", "continue running an
-outdated and thus potentially insecure kernel version for more than two weeks
-after a regression's culprit was identified", and "downgrade to a still
-supported kernel series that lack required features".
-
-How to realize this depends a lot on the situation. Here are a few rules of
-thumb for you, in order or importance:
-
- * Prioritize work on handling regression reports and fixing regression over all
- other Linux kernel work, unless the latter concerns acute security issues or
- bugs causing data loss or damage.
-
- * Always consider reverting the culprit commits and reapplying them later
- together with necessary fixes, as this might be the least dangerous and
- quickest way to fix a regression.
-
- * Developers should handle regressions in all supported kernel series, but are
- free to delegate the work to the stable team, if the issue probably at no
- point in time occurred with mainline.
-
- * Try to resolve any regressions introduced in the current development before
- its end. If you fear a fix might be too risky to apply only days before a new
- mainline release, let Linus decide: submit the fix separately to him as soon
- as possible with the explanation of the situation. He then can make a call
- and postpone the release if necessary, for example if multiple such changes
- show up in his inbox.
-
- * Address regressions in stable, longterm, or proper mainline releases with
- more urgency than regressions in mainline pre-releases. That changes after
- the release of the fifth pre-release, aka "-rc5": mainline then becomes as
- important, to ensure all the improvements and fixes are ideally tested
- together for at least one week before Linus releases a new mainline version.
-
- * Fix regressions within two or three days, if they are critical for some
- reason -- for example, if the issue is likely to affect many users of the
- kernel series in question on all or certain architectures. Note, this
- includes mainline, as issues like compile errors otherwise might prevent many
- testers or continuous integration systems from testing the series.
-
- * Aim to fix regressions within one week after the culprit was identified, if
- the issue was introduced in either:
-
- * a recent stable/longterm release
-
- * the development cycle of the latest proper mainline release
-
- In the latter case (say Linux v5.14), try to address regressions even
- quicker, if the stable series for the predecessor (v5.13) will be abandoned
- soon or already was stamped "End-of-Life" (EOL) -- this usually happens about
- three to four weeks after a new mainline release.
-
- * Try to fix all other regressions within two weeks after the culprit was
- found. Two or three additional weeks are acceptable for performance
- regressions and other issues which are annoying, but don't prevent anyone
- from running Linux (unless it's an issue in the current development cycle,
- as those should ideally be addressed before the release). A few weeks in
- total are acceptable if a regression can only be fixed with a risky change
- and at the same time is affecting only a few users; as much time is
- also okay if the regression is already present in the second newest longterm
- kernel series.
-
-Note: The aforementioned time frames for resolving regressions are meant to
-include getting the fix tested, reviewed, and merged into mainline, ideally with
-the fix being in linux-next at least briefly. This leads to delays you need to
-account for.
-
-Subsystem maintainers are expected to assist in reaching those periods by doing
-timely reviews and quick handling of accepted patches. They thus might have to
-send git-pull requests earlier or more often than usual; depending on the fix,
-it might even be acceptable to skip testing in linux-next. Especially fixes for
-regressions in stable and longterm kernels need to be handled quickly, as fixes
-need to be merged in mainline before they can be backported to older series.
+Expectations and best practices for fixing regressions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As a Linux kernel developer, you are expected to give your best to prevent
+situations where a regression caused by a recent change of yours leaves users
+only these options:
+
+ * Run a kernel with a regression that impacts usage.
+
+ * Switch to an older or newer kernel series.
+
+ * Continue running an outdated and thus potentially insecure kernel for more
+ than three weeks after the regression's culprit was identified. Ideally it
+ should be less than two. And it ought to be just a few days, if the issue is
+ severe or affects many users -- either in general or in prevalent
+ environments.
+
+How to realize that in practice depends on various factors. Use the following
+rules of thumb as a guide.
+
+In general:
+
+ * Prioritize work on regressions over all other Linux kernel work, unless the
+ latter concerns a severe issue (e.g. acute security vulnerability, data loss,
+ bricked hardware, ...).
+
+ * Expedite fixing mainline regressions that recently made it into a proper
+ mainline, stable, or longterm release (either directly or via backport).
+
+ * Do not consider regressions from the current cycle as something that can wait
+ till the end of the cycle, as the issue might discourage or prevent users and
+ CI systems from testing mainline now or generally.
+
+ * Work with the required care to avoid additional or bigger damage, even if
+ resolving an issue then might take longer than outlined below.
+
+On timing once the culprit of a regression is known:
+
+ * Aim to mainline a fix within two or three days, if the issue is severe or
+ bothering many users -- either in general or in prevalent conditions like a
+ particular hardware environment, distribution, or stable/longterm series.
+
+ * Aim to mainline a fix by Sunday after the next, if the culprit made it
+ into a recent mainline, stable, or longterm release (either directly or via
+ backport); if the culprit became known early during a week and is simple to
+ resolve, try to mainline the fix within the same week.
+
+ * For other regressions, aim to mainline fixes before the hindmost Sunday
+ within the next three weeks. One or two Sundays later are acceptable, if the
+ regression is something people can live with easily for a while -- like a
+ mild performance regression.
+
+ * It's strongly discouraged to delay mainlining regression fixes till the next
+ merge window, except when the fix is extraordinarily risky or when the
+ culprit was mainlined more than a year ago.
+
+On procedure:
+
+ * Always consider reverting the culprit, as it's often the quickest and least
+ dangerous way to fix a regression. Don't worry about mainlining a fixed
+ variant later: that should be straight-forward, as most of the code went
+ through review once already.
+
+ * Try to resolve any regressions introduced in mainline during the past
+ twelve months before the current development cycle ends: Linus wants such
+ regressions to be handled like those from the current cycle, unless fixing
+ bears unusual risks.
+
+ * Consider CCing Linus on discussions or patch review, if a regression seems
+ tangly. Do the same in precarious or urgent cases -- especially if the
+ subsystem maintainer might be unavailable. Also CC the stable team, when you
+ know such a regression made it into a mainline, stable, or longterm release.
+
+ * For urgent regressions, consider asking Linus to pick up the fix straight
+ from the mailing list: he is totally fine with that for uncontroversial
+ fixes. Ideally though such requests should happen in accordance with the
+ subsystem maintainers or come directly from them.
+
+ * In case you are unsure if a fix is worth the risk applying just days before
+ a new mainline release, send Linus a mail with the usual lists and people in
+ CC; in it, summarize the situation while asking him to consider picking up
+ the fix straight from the list. He then himself can make the call and when
+ needed even postpone the release. Such requests again should ideally happen
+ in accordance with the subsystem maintainers or come directly from them.
+
+Regarding stable and longterm kernels:
+
+ * You are free to leave regressions to the stable team, if they at no point in
+ time occurred with mainline or were fixed there already.
+
+ * If a regression made it into a proper mainline release during the past
+ twelve months, ensure to tag the fix with "Cc: stable@vger.kernel.org", as a
+ "Fixes:" tag alone does not guarantee a backport. Please add the same tag,
+ in case you know the culprit was backported to stable or longterm kernels.
+
+ * When receiving reports about regressions in recent stable or longterm kernel
+ series, please evaluate at least briefly if the issue might happen in current
+ mainline as well -- and if that seems likely, take hold of the report. If in
+ doubt, ask the reporter to check mainline.
+
+ * Whenever you want to swiftly resolve a regression that recently also made it
+ into a proper mainline, stable, or longterm release, fix it quickly in
+ mainline; when appropriate thus involve Linus to fast-track the fix (see
+ above). That's because the stable team normally does neither revert nor fix
+ any changes that cause the same problems in mainline.
+
+ * In case of urgent regression fixes you might want to ensure prompt
+ backporting by dropping the stable team a note once the fix was mainlined;
+ this is especially advisable during merge windows and shortly thereafter, as
+ the fix otherwise might land at the end of a huge patch queue.
+
+On patch flow:
+
+ * Developers, when trying to reach the time periods mentioned above, remember
+ to account for the time it takes to get fixes tested, reviewed, and merged by
+ Linus, ideally with them being in linux-next at least briefly. Hence, if a
+ fix is urgent, make it obvious to ensure others handle it appropriately.
+
+ * Reviewers, you are kindly asked to assist developers in reaching the time
+ periods mentioned above by reviewing regression fixes in a timely manner.
+
+ * Subsystem maintainers, you likewise are encouraged to expedite the handling
+ of regression fixes. Thus evaluate if skipping linux-next is an option for
+ the particular fix. Also consider sending git pull requests more often than
+ usual when needed. And try to avoid holding onto regression fixes over
+ weekends -- especially when the fix is marked for backporting.
More aspects regarding regressions developers should be aware of
See Documentation/process/email-clients.rst for recommendations on email
clients and mailing list etiquette.
+.. _interleaved_replies:
+
+Use trimmed interleaved replies in email discussions
+----------------------------------------------------
+Top-posting is strongly discouraged in Linux kernel development
+discussions. Interleaved (or "inline") replies make conversations much
+easier to follow. For more details see:
+https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
+
+As is frequently quoted on the mailing list::
+
+ A: http://en.wikipedia.org/wiki/Top_post
+ Q: Were do I find info about this thing called top-posting?
+ A: Because it messes up the order in which people normally read text.
+ Q: Why is top-posting such a bad thing?
+ A: Top-posting.
+ Q: What is the most annoying thing in e-mail?
+
+Similarly, please trim all unneeded quotations that aren't relevant
+to your reply. This makes responses easier to find, and saves time and
+space. For more details see: http://daringfireball.net/2007/07/on_top ::
+
+ A: No.
+ Q: Should I include quotations after my reply?
+
.. _resend_reminders:
Don't get discouraged - or impatient
as needed (or at least as we managed to add it — probably *not* all that is
needed).
+Human interfaces
+----------------
+
+.. toctree::
+ :maxdepth: 1
+
+ input/index
+ hid/index
+ sound/index
+ gpu/index
+ fb/index
+
+Storage interfaces
+------------------
+
+.. toctree::
+ :maxdepth: 1
+
+ filesystems/index
+ block/index
+ cdrom/index
+ scsi/index
+ target/index
+
**Fixme**: much more organizational work is needed here.
.. toctree::
core-api/index
locking/index
accounting/index
- block/index
- cdrom/index
cpu-freq/index
- fb/index
fpga/index
- hid/index
i2c/index
iio/index
isdn/index
networking/index
pcmcia/index
power/index
- target/index
timers/index
spi/index
w1/index
watchdog/index
virt/index
- input/index
hwmon/index
- gpu/index
accel/index
security/index
- sound/index
crypto/index
- filesystems/index
mm/index
bpf/index
usb/index
PCI/index
- scsi/index
misc-devices/index
scheduler/index
mhi/index
Default: Y
-The module parameters can be set from the debugfs files in::
+The module parameters can be set from the sysfs files in::
/sys/module/haltpoll/parameters/
| | function. | |
+-----------------------+---------------------------+-------------------------+
-These module parameters can be set from the debugfs files in:
+These module parameters can be set from the sysfs files in:
/sys/module/kvm/parameters/
-Note: that these module parameters are system wide values and are not able to
+Note: these module parameters are system-wide values and are not able to
be tuned on a per vm basis.
Any changes to these parameters will be picked up by new and existing vCPUs the
global max polling interval (halt_poll_ns) then the host will always poll for the
entire block time and thus cpu utilisation will go to 100%.
-- Halt polling essentially presents a trade off between power usage and latency and
+- Halt polling essentially presents a trade-off between power usage and latency and
the module parameters should be used to tune the affinity for this. Idle cpu time is
essentially converted to host kernel time with the aim of decreasing latency when
entering the guest.
- Halt polling will only be conducted by the host when no other tasks are runnable on
that cpu, otherwise the polling will cease immediately and schedule will be invoked to
- allow that other task to run. Thus this doesn't allow a guest to denial of service the
- cpu.
+ allow that other task to run. Thus this doesn't allow a guest to cause denial of service
+ of the cpu.
2. Write-Protection: The SPTE is present and the fault is caused by
write-protect. That means we just need to change the W bit of the spte.
-What we use to avoid all the race is the Host-writable bit and MMU-writable bit
+What we use to avoid all the races is the Host-writable bit and MMU-writable bit
on the spte:
- Host-writable means the gfn is writable in the host kernel page tables and in
A solution for indirect sp could be to pin the gfn, for example via
kvm_vcpu_gfn_to_pfn_atomic, before the cmpxchg. After the pinning:
-- We have held the refcount of pfn that means the pfn can not be freed and
+- We have held the refcount of pfn; that means the pfn can not be freed and
be reused for another gfn.
- The pfn is writable and therefore it cannot be shared between different gfns
by KSM.
The Dirty bit is lost in this case.
In order to avoid this kind of issue, we always treat the spte as "volatile"
-if it can be updated out of mmu-lock, see spte_has_volatile_bits(), it means,
+if it can be updated out of mmu-lock [see spte_has_volatile_bits()]; it means
the spte is always atomically updated in this case.
3) flush tlbs due to spte updated
-If the spte is updated from writable to readonly, we should flush all TLBs,
+If the spte is updated from writable to read-only, we should flush all TLBs,
otherwise rmap_write_protect will find a read-only spte, even though the
writable spte might be cached on a CPU's TLB.
As mentioned before, the spte can be updated to writable out of mmu-lock on
-fast page fault path, in order to easily audit the path, we see if TLBs need
-be flushed caused by this reason in mmu_spte_update() since this is a common
+fast page fault path. In order to easily audit the path, we see if TLBs needing
+to be flushed caused this reason in mmu_spte_update() since this is a common
function to update spte (present -> present).
Since the spte is "volatile" if it can be updated out of mmu-lock, we always
-atomically update the spte, the race caused by fast page fault can be avoided,
+atomically update the spte and the race caused by fast page fault can be avoided.
See the comments in spte_has_volatile_bits() and mmu_spte_update().
Lockless Access Tracking:
:Arch: x86
:Protects: wakeup_vcpus_on_cpu
:Comment: This is a per-CPU lock and it is used for VT-d posted-interrupts.
- When VT-d posted-interrupts is supported and the VM has assigned
+ When VT-d posted-interrupts are supported and the VM has assigned
devices, we put the blocked vCPU on the list blocked_vcpu_on_cpu
- protected by blocked_vcpu_on_cpu_lock, when VT-d hardware issues
+ protected by blocked_vcpu_on_cpu_lock. When VT-d hardware issues
wakeup notification event since external interrupts from the
assigned devices happens, we will find the vCPU on the list to
wakeup.
registers. Only if the host supports the additional features, make use of them.
The magic page layout is described by struct kvm_vcpu_arch_shared
-in arch/powerpc/include/asm/kvm_para.h.
+in arch/powerpc/include/uapi/asm/kvm_para.h.
Magic page features
===================
================
In addition to features that indicate whether a host is capable of a particular
-feature we also have a channel for a guest to tell the guest whether it's capable
+feature we also have a channel for a guest to tell the host whether it's capable
of something. This is what we call "flags".
Flags are passed to the host in the low 12 bits of the Effective Address.
====================
The "ld" and "std" instructions are transformed to "lwz" and "stw" instructions
-respectively on 32 bit systems with an added offset of 4 to accommodate for big
+respectively on 32-bit systems with an added offset of 4 to accommodate for big
endianness.
The following is a list of mapping the Linux kernel performs when running as
2) PAPR hypercalls
PAPR hypercalls are needed to run server PowerPC PAPR guests (-M pseries in QEMU).
-These are the same hypercalls that pHyp, the POWER hypervisor implements. Some of
+These are the same hypercalls that pHyp, the POWER hypervisor, implements. Some of
them are handled in the kernel, some are handled in user space. This is only
available on book3s_64.
However, VCPU request users should refrain from doing so, as it would
break the abstraction. The first 8 bits are reserved for architecture
-independent requests, all additional bits are available for architecture
+independent requests; all additional bits are available for architecture
dependent requests.
Architecture Independent Requests
This flag is applied to requests that only need immediate attention
from VCPUs running in guest mode. That is, sleeping VCPUs do not need
- to be awaken for these requests. Sleeping VCPUs will handle the
- requests when they are awaken later for some other reason.
+ to be awakened for these requests. Sleeping VCPUs will handle the
+ requests when they are awakened later for some other reason.
KVM_REQUEST_WAIT
X: Documentation/spi/
X: Documentation/userspace-api/media/
+DOCUMENTATION PROCESS
+M: Jonathan Corbet <corbet@lwn.net>
+S: Maintained
+F: Documentation/process/
+L: workflows@vger.kernel.org
+
DOCUMENTATION REPORTING ISSUES
M: Thorsten Leemhuis <linux@leemhuis.info>
L: linux-doc@vger.kernel.org
#ifndef __ASSEMBLY__
+/**
+ * IS_ERR_VALUE - Detect an error pointer.
+ * @x: The pointer to check.
+ *
+ * Like IS_ERR(), but does not generate a compiler warning if result is unused.
+ */
#define IS_ERR_VALUE(x) unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO)
+/**
+ * ERR_PTR - Create an error pointer.
+ * @error: A negative error code.
+ *
+ * Encodes @error into a pointer value. Users should consider the result
+ * opaque and not assume anything about how the error is encoded.
+ *
+ * Return: A pointer with @error encoded within its value.
+ */
static inline void * __must_check ERR_PTR(long error)
{
return (void *) error;
}
+/**
+ * PTR_ERR - Extract the error code from an error pointer.
+ * @ptr: An error pointer.
+ * Return: The error code within @ptr.
+ */
static inline long __must_check PTR_ERR(__force const void *ptr)
{
return (long) ptr;
}
+/**
+ * IS_ERR - Detect an error pointer.
+ * @ptr: The pointer to check.
+ * Return: true if @ptr is an error pointer, false otherwise.
+ */
static inline bool __must_check IS_ERR(__force const void *ptr)
{
return IS_ERR_VALUE((unsigned long)ptr);
}
+/**
+ * IS_ERR_OR_NULL - Detect an error pointer or a null pointer.
+ * @ptr: The pointer to check.
+ *
+ * Like IS_ERR(), but also returns true for a null pointer.
+ */
static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
{
return unlikely(!ptr) || IS_ERR_VALUE((unsigned long)ptr);
return (void *) ptr;
}
+/**
+ * PTR_ERR_OR_ZERO - Extract the error code from a pointer if it has one.
+ * @ptr: A potential error pointer.
+ *
+ * Convenience function that can be used inside a function that returns
+ * an error code to propagate errors received as error pointers.
+ * For example, ``return PTR_ERR_OR_ZERO(ptr);`` replaces:
+ *
+ * .. code-block:: c
+ *
+ * if (IS_ERR(ptr))
+ * return PTR_ERR(ptr);
+ * else
+ * return 0;
+ *
+ * Return: The error code within @ptr if it is an error pointer; 0 otherwise.
+ */
static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
{
if (IS_ERR(ptr))
projects / platform / kernel / linux-rpi.git / commitdiff