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x86/entry/32: Change INT80 to be an interrupt gate

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We want all of the syscall entries to run with interrupts off so that
we can efficiently run context tracking before enabling interrupts.

This will regress int $0x80 performance on 32-bit kernels by a
couple of cycles.  This shouldn't matter much -- int $0x80 is not a
fast path.

This effectively reverts:

  657c1eea00 ("x86/entry/32: Fix entry_INT80_32() to expect interrupts to be on")

... and fixes the same issue differently.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/59b4f90c9ebfccd8c937305dbbbca680bc74b905.1457558566.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2016-03-09 13:24:32 -08:00 committed by Ingo Molnar
parent fda57b2267
commit a798f09111
4 changed files with 9 additions and 18 deletions
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15
arch/x86/entry/common.c
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@ -371,14 +371,7 @@ __visible void do_syscall_64(struct pt_regs *regs)
* in workloads that use it, and it's usually called from * in workloads that use it, and it's usually called from
* do_fast_syscall_32, so forcibly inline it to improve performance. * do_fast_syscall_32, so forcibly inline it to improve performance.
*/ */
#ifdef CONFIG_X86_32 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
/* 32-bit kernels use a trap gate for INT80, and the asm code calls here. */
__visible
#else
/* 64-bit kernels use do_syscall_32_irqs_off() instead. */
static
#endif
__always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
{ {
struct thread_info *ti = pt_regs_to_thread_info(regs); struct thread_info *ti = pt_regs_to_thread_info(regs);
unsigned int nr = (unsigned int)regs->orig_ax; unsigned int nr = (unsigned int)regs->orig_ax;
@ -413,14 +406,12 @@ __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
syscall_return_slowpath(regs); syscall_return_slowpath(regs);
} }
#ifdef CONFIG_X86_64 /* Handles int $0x80 */
/* Handles INT80 on 64-bit kernels */ __visible void do_int80_syscall_32(struct pt_regs *regs)
__visible void do_syscall_32_irqs_off(struct pt_regs *regs)
{ {
local_irq_enable(); local_irq_enable();
do_syscall_32_irqs_on(regs); do_syscall_32_irqs_on(regs);
} }
#endif
/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible long do_fast_syscall_32(struct pt_regs *regs) __visible long do_fast_syscall_32(struct pt_regs *regs)

8
arch/x86/entry/entry_32.S
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@ -463,13 +463,13 @@ ENTRY(entry_INT80_32)
SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */ SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */
/* /*
* User mode is traced as though IRQs are on. Unlike the 64-bit * User mode is traced as though IRQs are on, and the interrupt gate
* case, INT80 is a trap gate on 32-bit kernels, so interrupts * turned them off.
* are already on (unless user code is messing around with iopl).
*/ */
TRACE_IRQS_OFF
movl %esp, %eax movl %esp, %eax
call do_syscall_32_irqs_on call do_int80_syscall_32
.Lsyscall_32_done: .Lsyscall_32_done:
restore_all: restore_all:

2
arch/x86/entry/entry_64_compat.S
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@ -336,7 +336,7 @@ ENTRY(entry_INT80_compat)
TRACE_IRQS_OFF TRACE_IRQS_OFF
movq %rsp, %rdi movq %rsp, %rdi
call do_syscall_32_irqs_off call do_int80_syscall_32
.Lsyscall_32_done: .Lsyscall_32_done:
/* Go back to user mode. */ /* Go back to user mode. */

2
arch/x86/kernel/traps.c
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@ -912,7 +912,7 @@ void __init trap_init(void)
#endif #endif
#ifdef CONFIG_X86_32 #ifdef CONFIG_X86_32
set_system_trap_gate(IA32_SYSCALL_VECTOR, entry_INT80_32); set_system_intr_gate(IA32_SYSCALL_VECTOR, entry_INT80_32);
set_bit(IA32_SYSCALL_VECTOR, used_vectors); set_bit(IA32_SYSCALL_VECTOR, used_vectors);
#endif #endif