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x86/entry/32: Filter NT and speed up AC filtering in SYSENTER 

This makes the 32-bit code work just like the 64-bit code.  It should
speed up syscalls on 32-bit kernels on Skylake by something like 20
cycles (by analogy to the 64-bit compat case).

It also cleans up NT just like we do for the 64-bit case.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
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: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/07daef3d44bd1ed62a2c866e143e8df64edb40ee.1457578375.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Andy Lutomirski 2016-03-09 19:00:26 -08:00 committed by Ingo Molnar
parent e786041153
commit 67f590e8d4
1 changed files with 22 additions and 1 deletions
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23
arch/x86/entry/entry_32.S
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@ -294,13 +294,29 @@ sysenter_past_esp:
pushl $__USER_DS /* pt_regs->ss */
pushl %ebp /* pt_regs->sp (stashed in bp) */
pushfl /* pt_regs->flags (except IF = 0) */
ASM_CLAC /* Clear AC after saving FLAGS */
orl $X86_EFLAGS_IF, (%esp) /* Fix IF */
pushl $__USER_CS /* pt_regs->cs */
pushl $0 /* pt_regs->ip = 0 (placeholder) */
pushl %eax /* pt_regs->orig_ax */
SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */
/*
* SYSENTER doesn't filter flags, so we need to clear NT and AC
* ourselves. To save a few cycles, we can check whether
* either was set instead of doing an unconditional popfq.
* This needs to happen before enabling interrupts so that
* we don't get preempted with NT set.
*
* NB.: .Lsysenter_fix_flags is a label with the code under it moved
* out-of-line as an optimization: NT is unlikely to be set in the
* majority of the cases and instead of polluting the I$ unnecessarily,
* we're keeping that code behind a branch which will predict as
* not-taken and therefore its instructions won't be fetched.
*/
testl $X86_EFLAGS_NT|X86_EFLAGS_AC, PT_EFLAGS(%esp)
jnz .Lsysenter_fix_flags
.Lsysenter_flags_fixed:
/*
* User mode is traced as though IRQs are on, and SYSENTER
* turned them off.
@ -339,6 +355,11 @@ sysenter_past_esp:
.popsection
_ASM_EXTABLE(1b, 2b)
PTGS_TO_GS_EX
.Lsysenter_fix_flags:
pushl $X86_EFLAGS_FIXED
popfl
jmp .Lsysenter_flags_fixed
ENDPROC(entry_SYSENTER_32)
# system call handler stub