Messages in this thread | | | Subject | Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support | Date | Fri, 5 Jan 2018 13:56:59 +0000 | From | "Woodhouse, David" <> |
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On Fri, 2018-01-05 at 13:54 +0100, Thomas Gleixner wrote: > On Thu, 4 Jan 2018, David Woodhouse wrote: > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h > > index 07cdd1715705..900fa7016d3f 100644 > > --- a/arch/x86/include/asm/cpufeatures.h > > +++ b/arch/x86/include/asm/cpufeatures.h > > @@ -342,5 +342,6 @@ > > #define X86_BUG_MONITOR X86_BUG(12) /* IPI required to wake up remote CPU */ > > #define X86_BUG_AMD_E400 X86_BUG(13) /* CPU is among the affected by Erratum 400 */ > > #define X86_BUG_CPU_INSECURE X86_BUG(14) /* CPU is insecure and needs kernel page table isolation */ > > +#define X86_BUG_NO_RETPOLINE X86_BUG(15) /* Placeholder: disable retpoline branch thunks */ > > I think this is the wrong approach. We have X86_BUG_CPU_INSECURE, which now > should be renamed to X86_BUG_CPU_MELTDOWN_V3 or something like that. It > tells the kernel, that the CPU is affected by variant 3.
As it says, it's a placeholder. The actual conditions depend on whether we decide to use IBRS or not, which also depends on whether we find IBRS_ATT or whether we're on Skylake+.
The IBRS patch series should be updating it.
> So what we really want is > > X86_BUG_MELTDOWN_V1/2/3 > > which get set when the CPU is affected by a particular variant and then > have feature flags > > X86_FEATURE_RETPOLINE > X86_FEATURE_IBRS > X86_FEATURE_NOSPEC
At some point during this whole painful mess, I had come to the conclusion that having relocations in altinstr didn't work, and that's why I had X86_xx_NO_RETPOLINE instead of X86_xx_RETPOLINE. I now think that something else was wrong when I was testing that, and relocs in altinstr do work. So sure, X86_FEATURE_RETPOLINE ought to work. I can change that round, and it's simpler for the IBRS patch set to take it into account and set it when appropriate. [unhandled content-type:application/x-pkcs7-signature] | |