Commit 67f590e8 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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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: default avatarAndy 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: default avatarIngo Molnar <mingo@kernel.org>
parent e7860411

arch/x86/entry/entry_32.S

+22 −1
Original line number Diff line number Diff line
@@ -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

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