On Fri, Apr 10, 2015 at 8:50 AM, Andi Kleen <a...@firstfloor.org> wrote: > From: Andi Kleen <a...@linux.intel.com> > > Every gs selector/index reload always paid an extra MFENCE > between the two SWAPGS. This was to work around an old > bug in early K8 steppings. All other CPUs don't need the extra > mfence. Patch the extra MFENCE only in for K8. > > Signed-off-by: Andi Kleen <a...@linux.intel.com> > --- > arch/x86/include/asm/cpufeature.h | 1 + > arch/x86/kernel/cpu/amd.c | 3 +++ > arch/x86/kernel/entry_64.S | 10 +++++++++- > 3 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/cpufeature.h > b/arch/x86/include/asm/cpufeature.h > index 90a5485..c695fad 100644 > --- a/arch/x86/include/asm/cpufeature.h > +++ b/arch/x86/include/asm/cpufeature.h > @@ -255,6 +255,7 @@ > #define X86_BUG_11AP X86_BUG(5) /* Bad local APIC aka 11AP */ > #define X86_BUG_FXSAVE_LEAK X86_BUG(6) /* FXSAVE leaks FOP/FIP/FOP */ > #define X86_BUG_CLFLUSH_MONITOR X86_BUG(7) /* AAI65, CLFLUSH required > before MONITOR */ > +#define X86_BUG_SWAPGS_MFENCE X86_BUG(8) /* SWAPGS may need MFENCE */ > > #if defined(__KERNEL__) && !defined(__ASSEMBLY__) > > diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c > index a220239..e7f5667 100644 > --- a/arch/x86/kernel/cpu/amd.c > +++ b/arch/x86/kernel/cpu/amd.c > @@ -551,6 +551,9 @@ static void init_amd_k8(struct cpuinfo_x86 *c) > if ((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58) > set_cpu_cap(c, X86_FEATURE_REP_GOOD); > > + /* Early steppings needed a mfence on swapgs. */ > + set_cpu_cap(c, X86_BUG_SWAPGS_MFENCE); > + > /* > * Some BIOSes incorrectly force this feature, but only K8 revision D > * (model = 0x14) and later actually support it. > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index 0b74ab0..bb44292 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -1212,13 +1212,21 @@ ENTRY(native_load_gs_index) > SWAPGS > gs_change: > movl %edi,%gs > -2: mfence /* workaround */ > +2: ASM_NOP3 /* may be replaced with mfence */
ALTERNATIVE, please. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
