1 /* SPDX-License-Identifier: GPL-2.0 */
3 * linux/arch/x86_64/entry.S
5 * Copyright (C) 1991, 1992 Linus Torvalds
6 * Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs
7 * Copyright (C) 2000 Pavel Machek <pavel@suse.cz>
9 * entry.S contains the system-call and fault low-level handling routines.
11 * Some of this is documented in Documentation/x86/entry_64.txt
13 * A note on terminology:
14 * - iret frame: Architecture defined interrupt frame from SS to RIP
15 * at the top of the kernel process stack.
18 * - ENTRY/END: Define functions in the symbol table.
19 * - TRACE_IRQ_*: Trace hardirq state for lock debugging.
20 * - idtentry: Define exception entry points.
22 #include <linux/linkage.h>
23 #include <asm/segment.h>
24 #include <asm/cache.h>
25 #include <asm/errno.h>
26 #include <asm/asm-offsets.h>
28 #include <asm/unistd.h>
29 #include <asm/thread_info.h>
30 #include <asm/hw_irq.h>
31 #include <asm/page_types.h>
32 #include <asm/irqflags.h>
33 #include <asm/paravirt.h>
34 #include <asm/percpu.h>
37 #include <asm/pgtable_types.h>
38 #include <asm/export.h>
39 #include <asm/frame.h>
40 #include <asm/nospec-branch.h>
41 #include <linux/err.h>
46 .section .entry.text, "ax"
48 #ifdef CONFIG_PARAVIRT
49 ENTRY(native_usergs_sysret64)
53 END(native_usergs_sysret64)
54 #endif /* CONFIG_PARAVIRT */
56 .macro TRACE_IRQS_FLAGS flags:req
57 #ifdef CONFIG_TRACE_IRQFLAGS
58 btl $9, \flags /* interrupts off? */
65 .macro TRACE_IRQS_IRETQ
66 TRACE_IRQS_FLAGS EFLAGS(%rsp)
70 * When dynamic function tracer is enabled it will add a breakpoint
71 * to all locations that it is about to modify, sync CPUs, update
72 * all the code, sync CPUs, then remove the breakpoints. In this time
73 * if lockdep is enabled, it might jump back into the debug handler
74 * outside the updating of the IST protection. (TRACE_IRQS_ON/OFF).
76 * We need to change the IDT table before calling TRACE_IRQS_ON/OFF to
77 * make sure the stack pointer does not get reset back to the top
78 * of the debug stack, and instead just reuses the current stack.
80 #if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS)
82 .macro TRACE_IRQS_OFF_DEBUG
83 call debug_stack_set_zero
85 call debug_stack_reset
88 .macro TRACE_IRQS_ON_DEBUG
89 call debug_stack_set_zero
91 call debug_stack_reset
94 .macro TRACE_IRQS_IRETQ_DEBUG
95 btl $9, EFLAGS(%rsp) /* interrupts off? */
102 # define TRACE_IRQS_OFF_DEBUG TRACE_IRQS_OFF
103 # define TRACE_IRQS_ON_DEBUG TRACE_IRQS_ON
104 # define TRACE_IRQS_IRETQ_DEBUG TRACE_IRQS_IRETQ
108 * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers.
110 * This is the only entry point used for 64-bit system calls. The
111 * hardware interface is reasonably well designed and the register to
112 * argument mapping Linux uses fits well with the registers that are
113 * available when SYSCALL is used.
115 * SYSCALL instructions can be found inlined in libc implementations as
116 * well as some other programs and libraries. There are also a handful
117 * of SYSCALL instructions in the vDSO used, for example, as a
118 * clock_gettimeofday fallback.
120 * 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11,
121 * then loads new ss, cs, and rip from previously programmed MSRs.
122 * rflags gets masked by a value from another MSR (so CLD and CLAC
123 * are not needed). SYSCALL does not save anything on the stack
124 * and does not change rsp.
126 * Registers on entry:
127 * rax system call number
129 * r11 saved rflags (note: r11 is callee-clobbered register in C ABI)
133 * r10 arg3 (needs to be moved to rcx to conform to C ABI)
136 * (note: r12-r15, rbp, rbx are callee-preserved in C ABI)
138 * Only called from user space.
140 * When user can change pt_regs->foo always force IRET. That is because
141 * it deals with uncanonical addresses better. SYSRET has trouble
142 * with them due to bugs in both AMD and Intel CPUs.
145 ENTRY(entry_SYSCALL_64)
148 * Interrupts are off on entry.
149 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
150 * it is too small to ever cause noticeable irq latency.
154 /* tss.sp2 is scratch space. */
155 movq %rsp, PER_CPU_VAR(cpu_tss_rw + TSS_sp2)
156 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
157 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
159 /* Construct struct pt_regs on stack */
160 pushq $__USER_DS /* pt_regs->ss */
161 pushq PER_CPU_VAR(cpu_tss_rw + TSS_sp2) /* pt_regs->sp */
162 pushq %r11 /* pt_regs->flags */
163 pushq $__USER_CS /* pt_regs->cs */
164 pushq %rcx /* pt_regs->ip */
165 GLOBAL(entry_SYSCALL_64_after_hwframe)
166 pushq %rax /* pt_regs->orig_ax */
168 PUSH_AND_CLEAR_REGS rax=$-ENOSYS
175 call do_syscall_64 /* returns with IRQs disabled */
177 TRACE_IRQS_IRETQ /* we're about to change IF */
180 * Try to use SYSRET instead of IRET if we're returning to
181 * a completely clean 64-bit userspace context. If we're not,
182 * go to the slow exit path.
187 cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */
188 jne swapgs_restore_regs_and_return_to_usermode
191 * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP
192 * in kernel space. This essentially lets the user take over
193 * the kernel, since userspace controls RSP.
195 * If width of "canonical tail" ever becomes variable, this will need
196 * to be updated to remain correct on both old and new CPUs.
198 * Change top bits to match most significant bit (47th or 56th bit
199 * depending on paging mode) in the address.
201 #ifdef CONFIG_X86_5LEVEL
202 ALTERNATIVE "shl $(64 - 48), %rcx; sar $(64 - 48), %rcx", \
203 "shl $(64 - 57), %rcx; sar $(64 - 57), %rcx", X86_FEATURE_LA57
205 shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
206 sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
209 /* If this changed %rcx, it was not canonical */
211 jne swapgs_restore_regs_and_return_to_usermode
213 cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */
214 jne swapgs_restore_regs_and_return_to_usermode
217 cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */
218 jne swapgs_restore_regs_and_return_to_usermode
221 * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot
222 * restore RF properly. If the slowpath sets it for whatever reason, we
223 * need to restore it correctly.
225 * SYSRET can restore TF, but unlike IRET, restoring TF results in a
226 * trap from userspace immediately after SYSRET. This would cause an
227 * infinite loop whenever #DB happens with register state that satisfies
228 * the opportunistic SYSRET conditions. For example, single-stepping
231 * movq $stuck_here, %rcx
236 * would never get past 'stuck_here'.
238 testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
239 jnz swapgs_restore_regs_and_return_to_usermode
241 /* nothing to check for RSP */
243 cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */
244 jne swapgs_restore_regs_and_return_to_usermode
247 * We win! This label is here just for ease of understanding
248 * perf profiles. Nothing jumps here.
250 syscall_return_via_sysret:
251 /* rcx and r11 are already restored (see code above) */
253 POP_REGS pop_rdi=0 skip_r11rcx=1
256 * Now all regs are restored except RSP and RDI.
257 * Save old stack pointer and switch to trampoline stack.
260 movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
262 pushq RSP-RDI(%rdi) /* RSP */
263 pushq (%rdi) /* RDI */
266 * We are on the trampoline stack. All regs except RDI are live.
267 * We can do future final exit work right here.
269 STACKLEAK_ERASE_NOCLOBBER
271 SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
276 END(entry_SYSCALL_64)
282 ENTRY(__switch_to_asm)
285 * Save callee-saved registers
286 * This must match the order in inactive_task_frame
296 movq %rsp, TASK_threadsp(%rdi)
297 movq TASK_threadsp(%rsi), %rsp
299 #ifdef CONFIG_STACKPROTECTOR
300 movq TASK_stack_canary(%rsi), %rbx
301 movq %rbx, PER_CPU_VAR(fixed_percpu_data) + stack_canary_offset
304 #ifdef CONFIG_RETPOLINE
306 * When switching from a shallower to a deeper call stack
307 * the RSB may either underflow or use entries populated
308 * with userspace addresses. On CPUs where those concerns
309 * exist, overwrite the RSB with entries which capture
310 * speculative execution to prevent attack.
312 FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
315 /* restore callee-saved registers */
327 * A newly forked process directly context switches into this address.
329 * rax: prev task we switched from
330 * rbx: kernel thread func (NULL for user thread)
331 * r12: kernel thread arg
336 call schedule_tail /* rdi: 'prev' task parameter */
338 testq %rbx, %rbx /* from kernel_thread? */
339 jnz 1f /* kernel threads are uncommon */
344 call syscall_return_slowpath /* returns with IRQs disabled */
345 TRACE_IRQS_ON /* user mode is traced as IRQS on */
346 jmp swapgs_restore_regs_and_return_to_usermode
354 * A kernel thread is allowed to return here after successfully
355 * calling do_execve(). Exit to userspace to complete the execve()
363 * Build the entry stubs with some assembler magic.
364 * We pack 1 stub into every 8-byte block.
367 ENTRY(irq_entries_start)
368 vector=FIRST_EXTERNAL_VECTOR
369 .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
370 UNWIND_HINT_IRET_REGS
371 pushq $(~vector+0x80) /* Note: always in signed byte range */
376 END(irq_entries_start)
378 .macro DEBUG_ENTRY_ASSERT_IRQS_OFF
379 #ifdef CONFIG_DEBUG_ENTRY
382 testl $X86_EFLAGS_IF, %eax
391 * Enters the IRQ stack if we're not already using it. NMI-safe. Clobbers
392 * flags and puts old RSP into old_rsp, and leaves all other GPRs alone.
393 * Requires kernel GSBASE.
395 * The invariant is that, if irq_count != -1, then the IRQ stack is in use.
397 .macro ENTER_IRQ_STACK regs=1 old_rsp save_ret=0
398 DEBUG_ENTRY_ASSERT_IRQS_OFF
402 * If save_ret is set, the original stack contains one additional
403 * entry -- the return address. Therefore, move the address one
404 * entry below %rsp to \old_rsp.
406 leaq 8(%rsp), \old_rsp
412 UNWIND_HINT_REGS base=\old_rsp
415 incl PER_CPU_VAR(irq_count)
416 jnz .Lirq_stack_push_old_rsp_\@
419 * Right now, if we just incremented irq_count to zero, we've
420 * claimed the IRQ stack but we haven't switched to it yet.
422 * If anything is added that can interrupt us here without using IST,
423 * it must be *extremely* careful to limit its stack usage. This
424 * could include kprobes and a hypothetical future IST-less #DB
427 * The OOPS unwinder relies on the word at the top of the IRQ
428 * stack linking back to the previous RSP for the entire time we're
429 * on the IRQ stack. For this to work reliably, we need to write
430 * it before we actually move ourselves to the IRQ stack.
433 movq \old_rsp, PER_CPU_VAR(irq_stack_backing_store + IRQ_STACK_SIZE - 8)
434 movq PER_CPU_VAR(hardirq_stack_ptr), %rsp
436 #ifdef CONFIG_DEBUG_ENTRY
438 * If the first movq above becomes wrong due to IRQ stack layout
439 * changes, the only way we'll notice is if we try to unwind right
440 * here. Assert that we set up the stack right to catch this type
443 cmpq -8(%rsp), \old_rsp
444 je .Lirq_stack_okay\@
449 .Lirq_stack_push_old_rsp_\@:
453 UNWIND_HINT_REGS indirect=1
458 * Push the return address to the stack. This return address can
459 * be found at the "real" original RSP, which was offset by 8 at
460 * the beginning of this macro.
467 * Undoes ENTER_IRQ_STACK.
469 .macro LEAVE_IRQ_STACK regs=1
470 DEBUG_ENTRY_ASSERT_IRQS_OFF
471 /* We need to be off the IRQ stack before decrementing irq_count. */
479 * As in ENTER_IRQ_STACK, irq_count == 0, we are still claiming
480 * the irq stack but we're not on it.
483 decl PER_CPU_VAR(irq_count)
487 * Interrupt entry helper function.
489 * Entry runs with interrupts off. Stack layout at entry:
490 * +----------------------------------------------------+
496 * +----------------------------------------------------+
497 * | regs->orig_ax = ~(interrupt number) |
498 * +----------------------------------------------------+
500 * +----------------------------------------------------+
502 ENTRY(interrupt_entry)
507 testb $3, CS-ORIG_RAX+8(%rsp)
512 * Switch to the thread stack. The IRET frame and orig_ax are
513 * on the stack, as well as the return address. RDI..R12 are
514 * not (yet) on the stack and space has not (yet) been
515 * allocated for them.
519 /* Need to switch before accessing the thread stack. */
520 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
522 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
525 * We have RDI, return address, and orig_ax on the stack on
526 * top of the IRET frame. That means offset=24
528 UNWIND_HINT_IRET_REGS base=%rdi offset=24
530 pushq 7*8(%rdi) /* regs->ss */
531 pushq 6*8(%rdi) /* regs->rsp */
532 pushq 5*8(%rdi) /* regs->eflags */
533 pushq 4*8(%rdi) /* regs->cs */
534 pushq 3*8(%rdi) /* regs->ip */
535 pushq 2*8(%rdi) /* regs->orig_ax */
536 pushq 8(%rdi) /* return address */
542 PUSH_AND_CLEAR_REGS save_ret=1
543 ENCODE_FRAME_POINTER 8
549 * IRQ from user mode.
551 * We need to tell lockdep that IRQs are off. We can't do this until
552 * we fix gsbase, and we should do it before enter_from_user_mode
553 * (which can take locks). Since TRACE_IRQS_OFF is idempotent,
554 * the simplest way to handle it is to just call it twice if
555 * we enter from user mode. There's no reason to optimize this since
556 * TRACE_IRQS_OFF is a no-op if lockdep is off.
560 CALL_enter_from_user_mode
563 ENTER_IRQ_STACK old_rsp=%rdi save_ret=1
564 /* We entered an interrupt context - irqs are off: */
569 _ASM_NOKPROBE(interrupt_entry)
572 /* Interrupt entry/exit. */
575 * The interrupt stubs push (~vector+0x80) onto the stack and
576 * then jump to common_interrupt.
578 .p2align CONFIG_X86_L1_CACHE_SHIFT
580 addq $-0x80, (%rsp) /* Adjust vector to [-256, -1] range */
582 UNWIND_HINT_REGS indirect=1
583 call do_IRQ /* rdi points to pt_regs */
584 /* 0(%rsp): old RSP */
586 DISABLE_INTERRUPTS(CLBR_ANY)
594 /* Interrupt came from user space */
597 call prepare_exit_to_usermode
600 GLOBAL(swapgs_restore_regs_and_return_to_usermode)
601 #ifdef CONFIG_DEBUG_ENTRY
602 /* Assert that pt_regs indicates user mode. */
611 * The stack is now user RDI, orig_ax, RIP, CS, EFLAGS, RSP, SS.
612 * Save old stack pointer and switch to trampoline stack.
615 movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
617 /* Copy the IRET frame to the trampoline stack. */
618 pushq 6*8(%rdi) /* SS */
619 pushq 5*8(%rdi) /* RSP */
620 pushq 4*8(%rdi) /* EFLAGS */
621 pushq 3*8(%rdi) /* CS */
622 pushq 2*8(%rdi) /* RIP */
624 /* Push user RDI on the trampoline stack. */
628 * We are on the trampoline stack. All regs except RDI are live.
629 * We can do future final exit work right here.
631 STACKLEAK_ERASE_NOCLOBBER
633 SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
641 /* Returning to kernel space */
643 #ifdef CONFIG_PREEMPT
644 /* Interrupts are off */
645 /* Check if we need preemption */
646 btl $9, EFLAGS(%rsp) /* were interrupts off? */
648 cmpl $0, PER_CPU_VAR(__preempt_count)
650 call preempt_schedule_irq
654 * The iretq could re-enable interrupts:
658 GLOBAL(restore_regs_and_return_to_kernel)
659 #ifdef CONFIG_DEBUG_ENTRY
660 /* Assert that pt_regs indicates kernel mode. */
667 addq $8, %rsp /* skip regs->orig_ax */
669 * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
670 * when returning from IPI handler.
675 UNWIND_HINT_IRET_REGS
677 * Are we returning to a stack segment from the LDT? Note: in
678 * 64-bit mode SS:RSP on the exception stack is always valid.
680 #ifdef CONFIG_X86_ESPFIX64
681 testb $4, (SS-RIP)(%rsp)
682 jnz native_irq_return_ldt
685 .global native_irq_return_iret
686 native_irq_return_iret:
688 * This may fault. Non-paranoid faults on return to userspace are
689 * handled by fixup_bad_iret. These include #SS, #GP, and #NP.
690 * Double-faults due to espfix64 are handled in do_double_fault.
691 * Other faults here are fatal.
695 #ifdef CONFIG_X86_ESPFIX64
696 native_irq_return_ldt:
698 * We are running with user GSBASE. All GPRs contain their user
699 * values. We have a percpu ESPFIX stack that is eight slots
700 * long (see ESPFIX_STACK_SIZE). espfix_waddr points to the bottom
701 * of the ESPFIX stack.
703 * We clobber RAX and RDI in this code. We stash RDI on the
704 * normal stack and RAX on the ESPFIX stack.
706 * The ESPFIX stack layout we set up looks like this:
708 * --- top of ESPFIX stack ---
713 * RIP <-- RSP points here when we're done
714 * RAX <-- espfix_waddr points here
715 * --- bottom of ESPFIX stack ---
718 pushq %rdi /* Stash user RDI */
719 SWAPGS /* to kernel GS */
720 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi /* to kernel CR3 */
722 movq PER_CPU_VAR(espfix_waddr), %rdi
723 movq %rax, (0*8)(%rdi) /* user RAX */
724 movq (1*8)(%rsp), %rax /* user RIP */
725 movq %rax, (1*8)(%rdi)
726 movq (2*8)(%rsp), %rax /* user CS */
727 movq %rax, (2*8)(%rdi)
728 movq (3*8)(%rsp), %rax /* user RFLAGS */
729 movq %rax, (3*8)(%rdi)
730 movq (5*8)(%rsp), %rax /* user SS */
731 movq %rax, (5*8)(%rdi)
732 movq (4*8)(%rsp), %rax /* user RSP */
733 movq %rax, (4*8)(%rdi)
734 /* Now RAX == RSP. */
736 andl $0xffff0000, %eax /* RAX = (RSP & 0xffff0000) */
739 * espfix_stack[31:16] == 0. The page tables are set up such that
740 * (espfix_stack | (X & 0xffff0000)) points to a read-only alias of
741 * espfix_waddr for any X. That is, there are 65536 RO aliases of
742 * the same page. Set up RSP so that RSP[31:16] contains the
743 * respective 16 bits of the /userspace/ RSP and RSP nonetheless
744 * still points to an RO alias of the ESPFIX stack.
746 orq PER_CPU_VAR(espfix_stack), %rax
748 SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
749 SWAPGS /* to user GS */
750 popq %rdi /* Restore user RDI */
753 UNWIND_HINT_IRET_REGS offset=8
756 * At this point, we cannot write to the stack any more, but we can
759 popq %rax /* Restore user RAX */
762 * RSP now points to an ordinary IRET frame, except that the page
763 * is read-only and RSP[31:16] are preloaded with the userspace
764 * values. We can now IRET back to userspace.
766 jmp native_irq_return_iret
768 END(common_interrupt)
769 _ASM_NOKPROBE(common_interrupt)
774 .macro apicinterrupt3 num sym do_sym
776 UNWIND_HINT_IRET_REGS
780 UNWIND_HINT_REGS indirect=1
781 call \do_sym /* rdi points to pt_regs */
787 /* Make sure APIC interrupt handlers end up in the irqentry section: */
788 #define PUSH_SECTION_IRQENTRY .pushsection .irqentry.text, "ax"
789 #define POP_SECTION_IRQENTRY .popsection
791 .macro apicinterrupt num sym do_sym
792 PUSH_SECTION_IRQENTRY
793 apicinterrupt3 \num \sym \do_sym
798 apicinterrupt3 IRQ_MOVE_CLEANUP_VECTOR irq_move_cleanup_interrupt smp_irq_move_cleanup_interrupt
799 apicinterrupt3 REBOOT_VECTOR reboot_interrupt smp_reboot_interrupt
803 apicinterrupt3 UV_BAU_MESSAGE uv_bau_message_intr1 uv_bau_message_interrupt
806 apicinterrupt LOCAL_TIMER_VECTOR apic_timer_interrupt smp_apic_timer_interrupt
807 apicinterrupt X86_PLATFORM_IPI_VECTOR x86_platform_ipi smp_x86_platform_ipi
809 #ifdef CONFIG_HAVE_KVM
810 apicinterrupt3 POSTED_INTR_VECTOR kvm_posted_intr_ipi smp_kvm_posted_intr_ipi
811 apicinterrupt3 POSTED_INTR_WAKEUP_VECTOR kvm_posted_intr_wakeup_ipi smp_kvm_posted_intr_wakeup_ipi
812 apicinterrupt3 POSTED_INTR_NESTED_VECTOR kvm_posted_intr_nested_ipi smp_kvm_posted_intr_nested_ipi
815 #ifdef CONFIG_X86_MCE_THRESHOLD
816 apicinterrupt THRESHOLD_APIC_VECTOR threshold_interrupt smp_threshold_interrupt
819 #ifdef CONFIG_X86_MCE_AMD
820 apicinterrupt DEFERRED_ERROR_VECTOR deferred_error_interrupt smp_deferred_error_interrupt
823 #ifdef CONFIG_X86_THERMAL_VECTOR
824 apicinterrupt THERMAL_APIC_VECTOR thermal_interrupt smp_thermal_interrupt
828 apicinterrupt CALL_FUNCTION_SINGLE_VECTOR call_function_single_interrupt smp_call_function_single_interrupt
829 apicinterrupt CALL_FUNCTION_VECTOR call_function_interrupt smp_call_function_interrupt
830 apicinterrupt RESCHEDULE_VECTOR reschedule_interrupt smp_reschedule_interrupt
833 apicinterrupt ERROR_APIC_VECTOR error_interrupt smp_error_interrupt
834 apicinterrupt SPURIOUS_APIC_VECTOR spurious_interrupt smp_spurious_interrupt
836 #ifdef CONFIG_IRQ_WORK
837 apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
841 * Exception entry points.
843 #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + (x) * 8)
846 * idtentry - Generate an IDT entry stub
847 * @sym: Name of the generated entry point
848 * @do_sym: C function to be called
849 * @has_error_code: True if this IDT vector has an error code on the stack
850 * @paranoid: non-zero means that this vector may be invoked from
851 * kernel mode with user GSBASE and/or user CR3.
852 * 2 is special -- see below.
853 * @shift_ist: Set to an IST index if entries from kernel mode should
854 * decrement the IST stack so that nested entries get a
855 * fresh stack. (This is for #DB, which has a nasty habit
858 * idtentry generates an IDT stub that sets up a usable kernel context,
859 * creates struct pt_regs, and calls @do_sym. The stub has the following
862 * On an entry from user mode, the stub switches from the trampoline or
863 * IST stack to the normal thread stack. On an exit to user mode, the
864 * normal exit-to-usermode path is invoked.
866 * On an exit to kernel mode, if @paranoid == 0, we check for preemption,
867 * whereas we omit the preemption check if @paranoid != 0. This is purely
868 * because the implementation is simpler this way. The kernel only needs
869 * to check for asynchronous kernel preemption when IRQ handlers return.
871 * If @paranoid == 0, then the stub will handle IRET faults by pretending
872 * that the fault came from user mode. It will handle gs_change faults by
873 * pretending that the fault happened with kernel GSBASE. Since this handling
874 * is omitted for @paranoid != 0, the #GP, #SS, and #NP stubs must have
875 * @paranoid == 0. This special handling will do the wrong thing for
876 * espfix-induced #DF on IRET, so #DF must not use @paranoid == 0.
878 * @paranoid == 2 is special: the stub will never switch stacks. This is for
879 * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS.
881 .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ist_offset=0 create_gap=0
883 UNWIND_HINT_IRET_REGS offset=\has_error_code*8
886 .if \shift_ist != -1 && \paranoid == 0
887 .error "using shift_ist requires paranoid=1"
892 .if \has_error_code == 0
893 pushq $-1 /* ORIG_RAX: no syscall to restart */
897 testb $3, CS-ORIG_RAX(%rsp) /* If coming from userspace, switch stacks */
898 jnz .Lfrom_usermode_switch_stack_\@
903 * If coming from kernel space, create a 6-word gap to allow the
904 * int3 handler to emulate a call instruction.
906 testb $3, CS-ORIG_RAX(%rsp)
907 jnz .Lfrom_usermode_no_gap_\@
911 UNWIND_HINT_IRET_REGS offset=8
912 .Lfrom_usermode_no_gap_\@:
921 /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */
925 TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */
931 movq %rsp, %rdi /* pt_regs pointer */
934 movq ORIG_RAX(%rsp), %rsi /* get error code */
935 movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
937 xorl %esi, %esi /* no error code */
941 subq $\ist_offset, CPU_TSS_IST(\shift_ist)
947 addq $\ist_offset, CPU_TSS_IST(\shift_ist)
950 /* these procedures expect "no swapgs" flag in ebx */
959 * Entry from userspace. Switch stacks and treat it
960 * as a normal entry. This means that paranoid handlers
961 * run in real process context if user_mode(regs).
963 .Lfrom_usermode_switch_stack_\@:
966 movq %rsp, %rdi /* pt_regs pointer */
969 movq ORIG_RAX(%rsp), %rsi /* get error code */
970 movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
972 xorl %esi, %esi /* no error code */
983 idtentry divide_error do_divide_error has_error_code=0
984 idtentry overflow do_overflow has_error_code=0
985 idtentry bounds do_bounds has_error_code=0
986 idtentry invalid_op do_invalid_op has_error_code=0
987 idtentry device_not_available do_device_not_available has_error_code=0
988 idtentry double_fault do_double_fault has_error_code=1 paranoid=2
989 idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0
990 idtentry invalid_TSS do_invalid_TSS has_error_code=1
991 idtentry segment_not_present do_segment_not_present has_error_code=1
992 idtentry spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0
993 idtentry coprocessor_error do_coprocessor_error has_error_code=0
994 idtentry alignment_check do_alignment_check has_error_code=1
995 idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0
999 * Reload gs selector with exception handling
1002 ENTRY(native_load_gs_index)
1005 DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
1010 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
1012 TRACE_IRQS_FLAGS (%rsp)
1016 ENDPROC(native_load_gs_index)
1017 EXPORT_SYMBOL(native_load_gs_index)
1019 _ASM_EXTABLE(.Lgs_change, bad_gs)
1020 .section .fixup, "ax"
1021 /* running with kernelgs */
1023 SWAPGS /* switch back to user gs */
1025 /* This can't be a string because the preprocessor needs to see it. */
1026 movl $__USER_DS, %eax
1029 ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG
1035 /* Call softirq on interrupt stack. Interrupts are off. */
1036 ENTRY(do_softirq_own_stack)
1039 ENTER_IRQ_STACK regs=0 old_rsp=%r11
1041 LEAVE_IRQ_STACK regs=0
1044 ENDPROC(do_softirq_own_stack)
1046 #ifdef CONFIG_XEN_PV
1047 idtentry hypervisor_callback xen_do_hypervisor_callback has_error_code=0
1050 * A note on the "critical region" in our callback handler.
1051 * We want to avoid stacking callback handlers due to events occurring
1052 * during handling of the last event. To do this, we keep events disabled
1053 * until we've done all processing. HOWEVER, we must enable events before
1054 * popping the stack frame (can't be done atomically) and so it would still
1055 * be possible to get enough handler activations to overflow the stack.
1056 * Although unlikely, bugs of that kind are hard to track down, so we'd
1057 * like to avoid the possibility.
1058 * So, on entry to the handler we detect whether we interrupted an
1059 * existing activation in its critical region -- if so, we pop the current
1060 * activation and restart the handler using the previous one.
1062 ENTRY(xen_do_hypervisor_callback) /* do_hypervisor_callback(struct *pt_regs) */
1065 * Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
1066 * see the correct pointer to the pt_regs
1069 movq %rdi, %rsp /* we don't return, adjust the stack frame */
1072 ENTER_IRQ_STACK old_rsp=%r10
1073 call xen_evtchn_do_upcall
1076 #ifndef CONFIG_PREEMPT
1077 call xen_maybe_preempt_hcall
1080 END(xen_do_hypervisor_callback)
1083 * Hypervisor uses this for application faults while it executes.
1084 * We get here for two reasons:
1085 * 1. Fault while reloading DS, ES, FS or GS
1086 * 2. Fault while executing IRET
1087 * Category 1 we do not need to fix up as Xen has already reloaded all segment
1088 * registers that could be reloaded and zeroed the others.
1089 * Category 2 we fix up by killing the current process. We cannot use the
1090 * normal Linux return path in this case because if we use the IRET hypercall
1091 * to pop the stack frame we end up in an infinite loop of failsafe callbacks.
1092 * We distinguish between categories by comparing each saved segment register
1093 * with its current contents: any discrepancy means we in category 1.
1095 ENTRY(xen_failsafe_callback)
1098 cmpw %cx, 0x10(%rsp)
1101 cmpw %cx, 0x18(%rsp)
1104 cmpw %cx, 0x20(%rsp)
1107 cmpw %cx, 0x28(%rsp)
1109 /* All segments match their saved values => Category 2 (Bad IRET). */
1114 UNWIND_HINT_IRET_REGS offset=8
1115 jmp general_protection
1116 1: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */
1120 UNWIND_HINT_IRET_REGS
1121 pushq $-1 /* orig_ax = -1 => not a system call */
1123 ENCODE_FRAME_POINTER
1125 END(xen_failsafe_callback)
1126 #endif /* CONFIG_XEN_PV */
1128 #ifdef CONFIG_XEN_PVHVM
1129 apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
1130 xen_hvm_callback_vector xen_evtchn_do_upcall
1134 #if IS_ENABLED(CONFIG_HYPERV)
1135 apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
1136 hyperv_callback_vector hyperv_vector_handler
1138 apicinterrupt3 HYPERV_REENLIGHTENMENT_VECTOR \
1139 hyperv_reenlightenment_vector hyperv_reenlightenment_intr
1141 apicinterrupt3 HYPERV_STIMER0_VECTOR \
1142 hv_stimer0_callback_vector hv_stimer0_vector_handler
1143 #endif /* CONFIG_HYPERV */
1145 idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=IST_INDEX_DB ist_offset=DB_STACK_OFFSET
1146 idtentry int3 do_int3 has_error_code=0 create_gap=1
1147 idtentry stack_segment do_stack_segment has_error_code=1
1149 #ifdef CONFIG_XEN_PV
1150 idtentry xennmi do_nmi has_error_code=0
1151 idtentry xendebug do_debug has_error_code=0
1152 idtentry xenint3 do_int3 has_error_code=0
1155 idtentry general_protection do_general_protection has_error_code=1
1156 idtentry page_fault do_page_fault has_error_code=1
1158 #ifdef CONFIG_KVM_GUEST
1159 idtentry async_page_fault do_async_page_fault has_error_code=1
1162 #ifdef CONFIG_X86_MCE
1163 idtentry machine_check do_mce has_error_code=0 paranoid=1
1167 * Save all registers in pt_regs, and switch gs if needed.
1168 * Use slow, but surefire "are we in kernel?" check.
1169 * Return: ebx=0: need swapgs on exit, ebx=1: otherwise
1171 ENTRY(paranoid_entry)
1174 PUSH_AND_CLEAR_REGS save_ret=1
1175 ENCODE_FRAME_POINTER 8
1179 * Always stash CR3 in %r14. This value will be restored,
1180 * verbatim, at exit. Needed if paranoid_entry interrupted
1181 * another entry that already switched to the user CR3 value
1182 * but has not yet returned to userspace.
1184 * This is also why CS (stashed in the "iret frame" by the
1185 * hardware at entry) can not be used: this may be a return
1186 * to kernel code, but with a user CR3 value.
1188 * Switching CR3 does not depend on kernel GSBASE so it can
1189 * be done before switching to the kernel GSBASE. This is
1190 * required for FSGSBASE because the kernel GSBASE has to
1191 * be retrieved from a kernel internal table.
1193 SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14
1195 /* EBX = 1 -> kernel GSBASE active, no restore required */
1198 * The kernel-enforced convention is a negative GSBASE indicates
1199 * a kernel value. No SWAPGS needed on entry and exit.
1201 movl $MSR_GS_BASE, %ecx
1204 jns .Lparanoid_entry_swapgs
1207 .Lparanoid_entry_swapgs:
1209 /* EBX = 0 -> SWAPGS required on exit */
1215 * "Paranoid" exit path from exception stack. This is invoked
1216 * only on return from non-NMI IST interrupts that came
1217 * from kernel space.
1219 * We may be returning to very strange contexts (e.g. very early
1220 * in syscall entry), so checking for preemption here would
1221 * be complicated. Fortunately, we there's no good reason
1222 * to try to handle preemption here.
1224 * On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it)
1226 ENTRY(paranoid_exit)
1228 DISABLE_INTERRUPTS(CLBR_ANY)
1229 TRACE_IRQS_OFF_DEBUG
1230 /* If EBX is 0, SWAPGS is required */
1232 jnz .Lparanoid_exit_no_swapgs
1234 /* Always restore stashed CR3 value (see paranoid_entry) */
1235 RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
1237 jmp .Lparanoid_exit_restore
1238 .Lparanoid_exit_no_swapgs:
1239 TRACE_IRQS_IRETQ_DEBUG
1240 /* Always restore stashed CR3 value (see paranoid_entry) */
1241 RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
1242 .Lparanoid_exit_restore:
1243 jmp restore_regs_and_return_to_kernel
1247 * Save all registers in pt_regs, and switch GS if needed.
1252 PUSH_AND_CLEAR_REGS save_ret=1
1253 ENCODE_FRAME_POINTER 8
1254 testb $3, CS+8(%rsp)
1255 jz .Lerror_kernelspace
1258 * We entered from user mode or we're pretending to have entered
1259 * from user mode due to an IRET fault.
1262 /* We have user CR3. Change to kernel CR3. */
1263 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
1265 .Lerror_entry_from_usermode_after_swapgs:
1266 /* Put us onto the real thread stack. */
1267 popq %r12 /* save return addr in %12 */
1268 movq %rsp, %rdi /* arg0 = pt_regs pointer */
1270 movq %rax, %rsp /* switch stack */
1271 ENCODE_FRAME_POINTER
1275 * We need to tell lockdep that IRQs are off. We can't do this until
1276 * we fix gsbase, and we should do it before enter_from_user_mode
1277 * (which can take locks).
1280 CALL_enter_from_user_mode
1288 * There are two places in the kernel that can potentially fault with
1289 * usergs. Handle them here. B stepping K8s sometimes report a
1290 * truncated RIP for IRET exceptions returning to compat mode. Check
1291 * for these here too.
1293 .Lerror_kernelspace:
1294 leaq native_irq_return_iret(%rip), %rcx
1295 cmpq %rcx, RIP+8(%rsp)
1297 movl %ecx, %eax /* zero extend */
1298 cmpq %rax, RIP+8(%rsp)
1300 cmpq $.Lgs_change, RIP+8(%rsp)
1301 jne .Lerror_entry_done
1304 * hack: .Lgs_change can fail with user gsbase. If this happens, fix up
1305 * gsbase and proceed. We'll fix up the exception and land in
1306 * .Lgs_change's error handler with kernel gsbase.
1309 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
1310 jmp .Lerror_entry_done
1313 /* Fix truncated RIP */
1314 movq %rcx, RIP+8(%rsp)
1319 * We came from an IRET to user mode, so we have user
1320 * gsbase and CR3. Switch to kernel gsbase and CR3:
1323 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
1326 * Pretend that the exception came from user mode: set up pt_regs
1327 * as if we faulted immediately after IRET.
1332 jmp .Lerror_entry_from_usermode_after_swapgs
1337 DISABLE_INTERRUPTS(CLBR_ANY)
1345 * Runs on exception stack. Xen PV does not go through this path at all,
1346 * so we can use real assembly here.
1349 * %r14: Used to save/restore the CR3 of the interrupted context
1350 * when PAGE_TABLE_ISOLATION is in use. Do not clobber.
1353 UNWIND_HINT_IRET_REGS
1356 * We allow breakpoints in NMIs. If a breakpoint occurs, then
1357 * the iretq it performs will take us out of NMI context.
1358 * This means that we can have nested NMIs where the next
1359 * NMI is using the top of the stack of the previous NMI. We
1360 * can't let it execute because the nested NMI will corrupt the
1361 * stack of the previous NMI. NMI handlers are not re-entrant
1364 * To handle this case we do the following:
1365 * Check the a special location on the stack that contains
1366 * a variable that is set when NMIs are executing.
1367 * The interrupted task's stack is also checked to see if it
1369 * If the variable is not set and the stack is not the NMI
1371 * o Set the special variable on the stack
1372 * o Copy the interrupt frame into an "outermost" location on the
1374 * o Copy the interrupt frame into an "iret" location on the stack
1375 * o Continue processing the NMI
1376 * If the variable is set or the previous stack is the NMI stack:
1377 * o Modify the "iret" location to jump to the repeat_nmi
1378 * o return back to the first NMI
1380 * Now on exit of the first NMI, we first clear the stack variable
1381 * The NMI stack will tell any nested NMIs at that point that it is
1382 * nested. Then we pop the stack normally with iret, and if there was
1383 * a nested NMI that updated the copy interrupt stack frame, a
1384 * jump will be made to the repeat_nmi code that will handle the second
1387 * However, espfix prevents us from directly returning to userspace
1388 * with a single IRET instruction. Similarly, IRET to user mode
1389 * can fault. We therefore handle NMIs from user space like
1390 * other IST entries.
1395 /* Use %rdx as our temp variable throughout */
1398 testb $3, CS-RIP+8(%rsp)
1399 jz .Lnmi_from_kernel
1402 * NMI from user mode. We need to run on the thread stack, but we
1403 * can't go through the normal entry paths: NMIs are masked, and
1404 * we don't want to enable interrupts, because then we'll end
1405 * up in an awkward situation in which IRQs are on but NMIs
1408 * We also must not push anything to the stack before switching
1409 * stacks lest we corrupt the "NMI executing" variable.
1414 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx
1416 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
1417 UNWIND_HINT_IRET_REGS base=%rdx offset=8
1418 pushq 5*8(%rdx) /* pt_regs->ss */
1419 pushq 4*8(%rdx) /* pt_regs->rsp */
1420 pushq 3*8(%rdx) /* pt_regs->flags */
1421 pushq 2*8(%rdx) /* pt_regs->cs */
1422 pushq 1*8(%rdx) /* pt_regs->rip */
1423 UNWIND_HINT_IRET_REGS
1424 pushq $-1 /* pt_regs->orig_ax */
1425 PUSH_AND_CLEAR_REGS rdx=(%rdx)
1426 ENCODE_FRAME_POINTER
1429 * At this point we no longer need to worry about stack damage
1430 * due to nesting -- we're on the normal thread stack and we're
1431 * done with the NMI stack.
1439 * Return back to user mode. We must *not* do the normal exit
1440 * work, because we don't want to enable interrupts.
1442 jmp swapgs_restore_regs_and_return_to_usermode
1446 * Here's what our stack frame will look like:
1447 * +---------------------------------------------------------+
1449 * | original Return RSP |
1450 * | original RFLAGS |
1453 * +---------------------------------------------------------+
1454 * | temp storage for rdx |
1455 * +---------------------------------------------------------+
1456 * | "NMI executing" variable |
1457 * +---------------------------------------------------------+
1458 * | iret SS } Copied from "outermost" frame |
1459 * | iret Return RSP } on each loop iteration; overwritten |
1460 * | iret RFLAGS } by a nested NMI to force another |
1461 * | iret CS } iteration if needed. |
1463 * +---------------------------------------------------------+
1464 * | outermost SS } initialized in first_nmi; |
1465 * | outermost Return RSP } will not be changed before |
1466 * | outermost RFLAGS } NMI processing is done. |
1467 * | outermost CS } Copied to "iret" frame on each |
1468 * | outermost RIP } iteration. |
1469 * +---------------------------------------------------------+
1471 * +---------------------------------------------------------+
1473 * The "original" frame is used by hardware. Before re-enabling
1474 * NMIs, we need to be done with it, and we need to leave enough
1475 * space for the asm code here.
1477 * We return by executing IRET while RSP points to the "iret" frame.
1478 * That will either return for real or it will loop back into NMI
1481 * The "outermost" frame is copied to the "iret" frame on each
1482 * iteration of the loop, so each iteration starts with the "iret"
1483 * frame pointing to the final return target.
1487 * Determine whether we're a nested NMI.
1489 * If we interrupted kernel code between repeat_nmi and
1490 * end_repeat_nmi, then we are a nested NMI. We must not
1491 * modify the "iret" frame because it's being written by
1492 * the outer NMI. That's okay; the outer NMI handler is
1493 * about to about to call do_nmi anyway, so we can just
1494 * resume the outer NMI.
1497 movq $repeat_nmi, %rdx
1500 movq $end_repeat_nmi, %rdx
1506 * Now check "NMI executing". If it's set, then we're nested.
1507 * This will not detect if we interrupted an outer NMI just
1514 * Now test if the previous stack was an NMI stack. This covers
1515 * the case where we interrupt an outer NMI after it clears
1516 * "NMI executing" but before IRET. We need to be careful, though:
1517 * there is one case in which RSP could point to the NMI stack
1518 * despite there being no NMI active: naughty userspace controls
1519 * RSP at the very beginning of the SYSCALL targets. We can
1520 * pull a fast one on naughty userspace, though: we program
1521 * SYSCALL to mask DF, so userspace cannot cause DF to be set
1522 * if it controls the kernel's RSP. We set DF before we clear
1526 /* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */
1527 cmpq %rdx, 4*8(%rsp)
1528 /* If the stack pointer is above the NMI stack, this is a normal NMI */
1531 subq $EXCEPTION_STKSZ, %rdx
1532 cmpq %rdx, 4*8(%rsp)
1533 /* If it is below the NMI stack, it is a normal NMI */
1536 /* Ah, it is within the NMI stack. */
1538 testb $(X86_EFLAGS_DF >> 8), (3*8 + 1)(%rsp)
1539 jz first_nmi /* RSP was user controlled. */
1541 /* This is a nested NMI. */
1545 * Modify the "iret" frame to point to repeat_nmi, forcing another
1546 * iteration of NMI handling.
1549 leaq -10*8(%rsp), %rdx
1556 /* Put stack back */
1562 /* We are returning to kernel mode, so this cannot result in a fault. */
1569 /* Make room for "NMI executing". */
1572 /* Leave room for the "iret" frame */
1575 /* Copy the "original" frame to the "outermost" frame */
1579 UNWIND_HINT_IRET_REGS
1581 /* Everything up to here is safe from nested NMIs */
1583 #ifdef CONFIG_DEBUG_ENTRY
1585 * For ease of testing, unmask NMIs right away. Disabled by
1586 * default because IRET is very expensive.
1589 pushq %rsp /* RSP (minus 8 because of the previous push) */
1590 addq $8, (%rsp) /* Fix up RSP */
1592 pushq $__KERNEL_CS /* CS */
1594 iretq /* continues at repeat_nmi below */
1595 UNWIND_HINT_IRET_REGS
1601 * If there was a nested NMI, the first NMI's iret will return
1602 * here. But NMIs are still enabled and we can take another
1603 * nested NMI. The nested NMI checks the interrupted RIP to see
1604 * if it is between repeat_nmi and end_repeat_nmi, and if so
1605 * it will just return, as we are about to repeat an NMI anyway.
1606 * This makes it safe to copy to the stack frame that a nested
1609 * RSP is pointing to "outermost RIP". gsbase is unknown, but, if
1610 * we're repeating an NMI, gsbase has the same value that it had on
1611 * the first iteration. paranoid_entry will load the kernel
1612 * gsbase if needed before we call do_nmi. "NMI executing"
1615 movq $1, 10*8(%rsp) /* Set "NMI executing". */
1618 * Copy the "outermost" frame to the "iret" frame. NMIs that nest
1619 * here must not modify the "iret" frame while we're writing to
1620 * it or it will end up containing garbage.
1630 * Everything below this point can be preempted by a nested NMI.
1631 * If this happens, then the inner NMI will change the "iret"
1632 * frame to point back to repeat_nmi.
1634 pushq $-1 /* ORIG_RAX: no syscall to restart */
1637 * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit
1638 * as we should not be calling schedule in NMI context.
1639 * Even with normal interrupts enabled. An NMI should not be
1640 * setting NEED_RESCHED or anything that normal interrupts and
1641 * exceptions might do.
1646 /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
1651 /* Always restore stashed CR3 value (see paranoid_entry) */
1652 RESTORE_CR3 scratch_reg=%r15 save_reg=%r14
1654 testl %ebx, %ebx /* swapgs needed? */
1662 * Skip orig_ax and the "outermost" frame to point RSP at the "iret"
1663 * at the "iret" frame.
1668 * Clear "NMI executing". Set DF first so that we can easily
1669 * distinguish the remaining code between here and IRET from
1670 * the SYSCALL entry and exit paths.
1672 * We arguably should just inspect RIP instead, but I (Andy) wrote
1673 * this code when I had the misapprehension that Xen PV supported
1674 * NMIs, and Xen PV would break that approach.
1677 movq $0, 5*8(%rsp) /* clear "NMI executing" */
1680 * iretq reads the "iret" frame and exits the NMI stack in a
1681 * single instruction. We are returning to kernel mode, so this
1682 * cannot result in a fault. Similarly, we don't need to worry
1683 * about espfix64 on the way back to kernel mode.
1688 ENTRY(ignore_sysret)
1694 ENTRY(rewind_stack_do_exit)
1696 /* Prevent any naive code from trying to unwind to our caller. */
1699 movq PER_CPU_VAR(cpu_current_top_of_stack), %rax
1700 leaq -PTREGS_SIZE(%rax), %rsp
1701 UNWIND_HINT_FUNC sp_offset=PTREGS_SIZE
1704 END(rewind_stack_do_exit)