On 10/01/2014 08:22 AM, H. Peter Anvin wrote: > On 09/30/2014 09:51 PM, Andy Lutomirski wrote: >> >> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S >> index 4299eb05023c..44d1dd371454 100644 >> --- a/arch/x86/ia32/ia32entry.S >> +++ b/arch/x86/ia32/ia32entry.S >> @@ -151,6 +151,18 @@ ENTRY(ia32_sysenter_target) >> 1: movl (%rbp),%ebp >> _ASM_EXTABLE(1b,ia32_badarg) >> ASM_CLAC >> + >> + /* >> + * Sysenter doesn't filter flags, so we need to clear NT >> + * ourselves. To save a few cycles, we can check whether >> + * NT was set instead of doing an unconditional popfq. >> + */ >> + testl $X86_EFLAGS_NT,EFLAGS(%rsp) /* saved EFLAGS match cpu */ >> + jz 1f >> + pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_FIXED) >> + popfq_cfi >> +1: >> + > > I'm wondering if it would be easier to just remove ASM_CLAC and do this > unconditionally. On SMAP-enabled hardware then that gives us back some > of the cycles, may make the branch unnecessary. > Heck, we can drop the CLD and the STI as well (with some tweaking in ia32_badarg.) -hpa -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html