Commit-ID: 092c74e420952c7cb68141731f2b562245b51eeb Gitweb: http://git.kernel.org/tip/092c74e420952c7cb68141731f2b562245b51eeb Author: Brian Gerst <brge...@gmail.com> AuthorDate: Wed, 4 May 2016 22:44:36 -0400 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 5 May 2016 08:37:30 +0200
x86/entry, sched/x86: Don't save/restore EFLAGS on task switch 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 <brge...@gmail.com> Acked-by: Andy Lutomirski <l...@kernel.org> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Borislav Petkov <b...@alien8.de> Cc: Borislav Petkov <b...@suse.de> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/1462416278-11974-2-git-send-email-brge...@gmail.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/entry/entry_32.S | 4 ---- arch/x86/entry/entry_64.S | 3 --- arch/x86/include/asm/switch_to.h | 4 +--- 3 files changed, 1 insertion(+), 10 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 10868aa..c84d99b 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -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) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 6344629..9ee0da1 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -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? */ diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h index 751bf4b..8f321a1 100644 --- a/arch/x86/include/asm/switch_to.h +++ b/arch/x86/include/asm/switch_to.h @@ -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), \
