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

Now that we have objtool validating AC=1 state for all x86_64 code,
we can once again guarantee clean flags on schedule.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 4fe27b6..1f0efdb 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -291,7 +291,6 @@ ENTRY(__switch_to_asm)
        pushq   %r13
        pushq   %r14
        pushq   %r15
-       pushfq
 
        /* switch stack */
        movq    %rsp, TASK_threadsp(%rdi)
@@ -314,7 +313,6 @@ ENTRY(__switch_to_asm)
 #endif
 
        /* restore callee-saved registers */
-       popfq
        popq    %r15
        popq    %r14
        popq    %r13

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 157149d..18a4b68 100644 (file)
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -40,13 +40,13 @@ asmlinkage void ret_from_fork(void);
  * order of the fields must match the code in __switch_to_asm().
  */
 struct inactive_task_frame {
-       unsigned long flags;
 #ifdef CONFIG_X86_64
        unsigned long r15;
        unsigned long r14;
        unsigned long r13;
        unsigned long r12;
 #else
+       unsigned long flags;
        unsigned long si;
        unsigned long di;
 #endif

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 026a43b..844a28b 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -393,13 +393,6 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
        fork_frame = container_of(childregs, struct fork_frame, regs);
        frame = &fork_frame->frame;
 
-       /*
-        * For a new task use the RESET flags value since there is no before.
-        * All the status flags are zero; DF and all the system flags must also
-        * be 0, specifically IF must be 0 because we context switch to the new
-        * task with interrupts disabled.
-        */
-       frame->flags = X86_EFLAGS_FIXED;
        frame->bp = 0;
        frame->ret_addr = (unsigned long) ret_from_fork;
        p->thread.sp = (unsigned long) fork_frame;