Re: [PATCH 1/7] KVM: x86: add SPEC_CTRL and IBPB_SUPPORT accessors

[Paolo Bonzini]

On 09/01/2018 12:14, David Hildenbrand wrote:
>>  
>> +/* These are scattered features in cpufeatures.h. */
>> +#define KVM_CPUID_BIT_AVX512_4VNNIW	2
>> +#define KVM_CPUID_BIT_AVX512_4FMAPS	3
>> +#define KVM_CPUID_BIT_SPEC_CTRL		26
>> +#define KVM_CPUID_BIT_STIBP		27
> I can see that STIBP is never checked in KVM code but only forwarded to
> the guest if available.
> 
> I am wondering if we would have to check against that, too, before
> issuing a FEATURE_SET_IBPB.

STIBP is "single-threaded indirect branch prediction".  SPEC_CTRL always
implies that FEATURE_SET_IBPB is available.

Paolo