Commit 2c7577a7 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

sched/x86_64: Don't save flags on context switch

Now that the kernel always runs with clean flags (in particular,
NT is clear), there is no need to save and restore flags on
every context switch.
Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Cc: Sebastian Lackner <sebastian@fds-team.de>
Cc: Anish Bhatt <anish@chelsio.com>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/bf6fb790787eb95b922157838f52712c25dda157.1412187233.git.luto@amacapital.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent cac7f242
...@@ -79,12 +79,12 @@ do { \ ...@@ -79,12 +79,12 @@ do { \
#else /* CONFIG_X86_32 */ #else /* CONFIG_X86_32 */
/* frame pointer must be last for get_wchan */ /* frame pointer must be last for get_wchan */
#define SAVE_CONTEXT "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t" #define SAVE_CONTEXT "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t" #define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
#define __EXTRA_CLOBBER \ #define __EXTRA_CLOBBER \
, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \ , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
"r12", "r13", "r14", "r15" "r12", "r13", "r14", "r15", "flags"
#ifdef CONFIG_CC_STACKPROTECTOR #ifdef CONFIG_CC_STACKPROTECTOR
#define __switch_canary \ #define __switch_canary \
...@@ -100,7 +100,11 @@ do { \ ...@@ -100,7 +100,11 @@ do { \
#define __switch_canary_iparam #define __switch_canary_iparam
#endif /* CC_STACKPROTECTOR */ #endif /* CC_STACKPROTECTOR */
/* Save restore flags to clear handle leaking NT */ /*
* There is no need to save or restore flags, because flags are always
* clean in kernel mode, with the possible exception of IOPL. Kernel IOPL
* has no effect.
*/
#define switch_to(prev, next, last) \ #define switch_to(prev, next, last) \
asm volatile(SAVE_CONTEXT \ asm volatile(SAVE_CONTEXT \
"movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \ "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \
......
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