63 lines
2.2 KiB
Diff
63 lines
2.2 KiB
Diff
From 512255a2ad2c832ca7d4de9f31245f73781922d0 Mon Sep 17 00:00:00 2001
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From: Andy Lutomirski <luto@kernel.org>
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Date: Mon, 17 Aug 2015 12:22:50 -0700
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Subject: [PATCH] Revert "sched/x86_64: Don't save flags on context switch"
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This reverts commit:
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2c7577a75837 ("sched/x86_64: Don't save flags on context switch")
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It was a nice speedup. It's also not quite correct: SYSENTER
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enables interrupts too early.
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We can re-add this optimization once the SYSENTER code is beaten
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into shape, which should happen in 4.3 or 4.4.
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Signed-off-by: Andy Lutomirski <luto@kernel.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Cc: stable@vger.kernel.org # v3.19
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Link: http://lkml.kernel.org/r/85f56651f59f76624e80785a8fd3bdfdd089a818.1439838962.git.luto@kernel.org
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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---
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arch/x86/include/asm/switch_to.h | 12 ++++--------
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1 file changed, 4 insertions(+), 8 deletions(-)
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diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
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index 751bf4b7bf11..d7f3b3b78ac3 100644
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--- a/arch/x86/include/asm/switch_to.h
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+++ b/arch/x86/include/asm/switch_to.h
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@@ -79,12 +79,12 @@ do { \
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#else /* CONFIG_X86_32 */
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/* frame pointer must be last for get_wchan */
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-#define SAVE_CONTEXT "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
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-#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
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+#define SAVE_CONTEXT "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
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+#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"
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#define __EXTRA_CLOBBER \
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, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
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- "r12", "r13", "r14", "r15", "flags"
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+ "r12", "r13", "r14", "r15"
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#ifdef CONFIG_CC_STACKPROTECTOR
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#define __switch_canary \
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@@ -100,11 +100,7 @@ do { \
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#define __switch_canary_iparam
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#endif /* CC_STACKPROTECTOR */
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-/*
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- * There is no need to save or restore flags, because flags are always
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- * clean in kernel mode, with the possible exception of IOPL. Kernel IOPL
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- * has no effect.
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- */
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+/* Save restore flags to clear handle leaking NT */
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#define switch_to(prev, next, last) \
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asm volatile(SAVE_CONTEXT \
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"movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \
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--
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2.4.3
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