Messages in this thread | | | Date | Mon, 17 Jan 2022 18:31:58 +0100 | Subject | Re: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing | From | Paolo Bonzini <> |
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On 1/17/22 08:45, Like Xu wrote: > From: Like Xu <likexu@tencent.com> > > According to Intel extended feature disable (XFD) spec, the sub-function i > (i > 1) of CPUID function 0DH enumerates "details for state component i. > ECX[2] enumerates support for XFD support for this state component." > > If KVM does not report F(XFD) feature (e.g. due to CONFIG_X86_64), > then the corresponding XFD support for any state component i > should also be removed. Translate this dependency into KVM terms. > > Fixes: 690a757d610e ("kvm: x86: Add CPUID support for Intel AMX") > Signed-off-by: Like Xu <likexu@tencent.com> > --- > arch/x86/kvm/cpuid.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index c55e57b30e81..e96efef4f048 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -886,6 +886,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > --array->nent; > continue; > } > + > + if (!kvm_cpu_cap_has(X86_FEATURE_XFD)) > + entry->ecx &= ~BIT_ULL(2); > entry->edx = 0; > } > break;
Generally this is something that is left to userspace. Apart from the usecase of "call KVM_GET_SUPPORTED_CPUID and pass it to KVM_SET_CPUID2", userspace should know what any changed bits mean.
Paolo
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