If you haven't pushed this out yet, I would hold off. I think it may be unnecessary.
--Andy On Thu, Aug 27, 2015 at 3:12 PM, Kamal Mostafa <[email protected]> wrote: > 3.19.8-ckt6 -stable review patch. If anyone has any objections, please let > me know. > > ------------------ > > From: Andy Lutomirski <[email protected]> > > commit 512255a2ad2c832ca7d4de9f31245f73781922d0 upstream. > > This reverts commit: > > 2c7577a75837 ("sched/x86_64: Don't save flags on context switch") > > It was a nice speedup. It's also not quite correct: SYSENTER > enables interrupts too early. > > We can re-add this optimization once the SYSENTER code is beaten > into shape, which should happen in 4.3 or 4.4. > > Signed-off-by: Andy Lutomirski <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Link: > http://lkml.kernel.org/r/85f56651f59f76624e80785a8fd3bdfdd089a818.1439838962.git.l...@kernel.org > Signed-off-by: Ingo Molnar <[email protected]> > Signed-off-by: Kamal Mostafa <[email protected]> > --- > arch/x86/include/asm/switch_to.h | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/include/asm/switch_to.h > b/arch/x86/include/asm/switch_to.h > index 751bf4b..d7f3b3b 100644 > --- a/arch/x86/include/asm/switch_to.h > +++ b/arch/x86/include/asm/switch_to.h > @@ -79,12 +79,12 @@ do { > \ > #else /* CONFIG_X86_32 */ > > /* frame pointer must be last for get_wchan */ > -#define SAVE_CONTEXT "pushq %%rbp ; movq %%rsi,%%rbp\n\t" > -#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t" > +#define SAVE_CONTEXT "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t" > +#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t" > > #define __EXTRA_CLOBBER \ > , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \ > - "r12", "r13", "r14", "r15", "flags" > + "r12", "r13", "r14", "r15" > > #ifdef CONFIG_CC_STACKPROTECTOR > #define __switch_canary > \ > @@ -100,11 +100,7 @@ do { > \ > #define __switch_canary_iparam > #endif /* CC_STACKPROTECTOR */ > > -/* > - * 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. > - */ > +/* Save restore flags to clear handle leaking NT */ > #define switch_to(prev, next, last) \ > asm volatile(SAVE_CONTEXT \ > "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \ > -- > 1.9.1 > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
