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 <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>

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 10868aa734dc07e9a438bcdd3d4c7b4aae0106d3..c84d99bfff94e2dc66f1e03cf752459dc8489022 100644 (file)
--- 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 6344629ae1ce7d03eedd401d81e96032696c64b2..9ee0da1807edff462536e3628e1db217bb835cd8 100644 (file)
--- 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 751bf4b7bf114da12231a56f4217c2583ddeafb2..8f321a1b03a1aaa0e87c4c1182d2b2f282efa1e4 100644 (file)
--- 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),                \