> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index 26110c202b19..950ec50f77c3 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -4115,7 +4115,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct
> > msr_data *msr_info)
> > break;
> > case MSR_IA32_SPEC_CTRL:
> > if (!msr_info->host_initiated &&
> > - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))
> > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&
> > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
>
> Shouldn't the IBRS/SSBD check be an "or" check? I don't think it's
> necessarily true that IBRS and SSBD have to both be set. Maybe something
> like:
>
> if (!msr_info->host_initiated &&
> !(guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) ||
> guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
>
> Does that make sense?
The '!' on each of the CPUID and '&&' make this the same. See:
AMD_IBRS set | AMD_SSBD set | !AMD_IBRS && !AMD_SSBD | !(AMD_IBRS ||
AMD_SSBD)
0 | 0 | 1 && 1 -> return 1 | !(0) -> 1 -> return 1
1 | 0 | 0 && 1, continue | !(1 || 0) -> continue
1 | 1 | 0 && 0, continue | !(1 || 1) -> continue
0 | 1 | 1 && 0, continue | !(0 || 1) -> continue
Meaning we will return 1 if:
the host has not initiator it or,
the guest CPUID does not have AMD_IBRS flag or,
the guest CPUID does not have AMD SSBD flag
I am fine modifying it the way you had in mind, but in the past the logic
was to use ! and &&, hence stuck to that.
>
> > return 1;
> >
> > msr_info->data = svm->spec_ctrl;
> > @@ -4217,11 +4218,12 @@ static int svm_set_msr(struct kvm_vcpu *vcpu,
> > struct msr_data *msr)
> > break;
> > case MSR_IA32_SPEC_CTRL:
> > if (!msr->host_initiated &&
> > - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))
> > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&
> > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
>
> Same question as above.
>
> Thanks,
> Tom
>
> > return 1;
> >
> > /* The STIBP bit doesn't fault even if it's not advertised */
> > - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))
> > + if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD))
> > return 1;
> >
> > svm->spec_ctrl = data;
> >
