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x86/entry, sched/x86: Don't save/restore EFLAGS on task switch

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Now that NT is filtered by the SYSENTER entry code, it is safe to skip saving and
restoring flags on task switch.  Also remove a leftover reset of flags on 64-bit
fork.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1462416278-11974-2-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Brian Gerst 2016-05-04 22:44:36 -04:00 committed by Ingo Molnar
parent 1fb48f8e54
commit 092c74e420
3 changed files with 1 additions and 10 deletions
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4
arch/x86/entry/entry_32.S
View File

@ -209,8 +209,6 @@ ENTRY(ret_from_fork)
call schedule_tail
GET_THREAD_INFO(%ebp)
popl %eax
pushl $0x0202 # Reset kernel eflags
popfl
/* When we fork, we trace the syscall return in the child, too. */
movl %esp, %eax
@ -223,8 +221,6 @@ ENTRY(ret_from_kernel_thread)
call schedule_tail
GET_THREAD_INFO(%ebp)
popl %eax
pushl $0x0202 # Reset kernel eflags
popfl
movl PT_EBP(%esp), %eax
call *PT_EBX(%esp)
movl $0, PT_EAX(%esp)

3
arch/x86/entry/entry_64.S
View File

@ -372,9 +372,6 @@ END(ptregs_\func)
ENTRY(ret_from_fork)
LOCK ; btr $TIF_FORK, TI_flags(%r8)
pushq $0x0002
popfq /* reset kernel eflags */
call schedule_tail /* rdi: 'prev' task parameter */
testb $3, CS(%rsp) /* from kernel_thread? */

4
arch/x86/include/asm/switch_to.h
View File

@ -39,8 +39,7 @@ do { \
*/ \
unsigned long ebx, ecx, edx, esi, edi; \
\
asm volatile("pushfl\n\t" /* save flags */ \
"pushl %%ebp\n\t" /* save EBP */ \
asm volatile("pushl %%ebp\n\t" /* save EBP */ \
"movl %%esp,%[prev_sp]\n\t" /* save ESP */ \
"movl %[next_sp],%%esp\n\t" /* restore ESP */ \
"movl $1f,%[prev_ip]\n\t" /* save EIP */ \
@ -49,7 +48,6 @@ do { \
"jmp __switch_to\n" /* regparm call */ \
"1:\t" \
"popl %%ebp\n\t" /* restore EBP */ \
"popfl\n" /* restore flags */ \
\
/* output parameters */ \
: [prev_sp] "=m" (prev->thread.sp), \