>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>index 0fc5e6312e93..d77b030e996c 100644
>--- a/arch/x86/include/asm/kvm_host.h
>+++ b/arch/x86/include/asm/kvm_host.h
>@@ -803,6 +803,7 @@ struct kvm_vcpu_arch {
>
> u64 xcr0;
> u64 guest_supported_xcr0;
>+ u64 guest_supported_xss;
This structure has the ia32_xss field. how about moving it here for symmetry?
>
> struct kvm_pio_request pio;
> void *pio_data;
>diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>index 1f206caec559..4e7a820cba62 100644
>--- a/arch/x86/kvm/cpuid.c
>+++ b/arch/x86/kvm/cpuid.c
>@@ -275,7 +275,8 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e
> best = cpuid_entry2_find(entries, nent, 0xD, 1);
> if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
> cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
>- best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
>+ best->ebx = xstate_required_size(vcpu->arch.xcr0 |
>+ vcpu->arch.ia32_xss, true);
>
> best = __kvm_find_kvm_cpuid_features(vcpu, entries, nent);
> if (kvm_hlt_in_guest(vcpu->kvm) && best &&
>@@ -312,6 +313,17 @@ static u64 vcpu_get_supported_xcr0(struct kvm_vcpu *vcpu)
> return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
> }
>
>+static u64 vcpu_get_supported_xss(struct kvm_vcpu *vcpu)
>+{
>+ struct kvm_cpuid_entry2 *best;
>+
>+ best = kvm_find_cpuid_entry_index(vcpu, 0xd, 1);
>+ if (!best)
>+ return 0;
>+
>+ return (best->ecx | ((u64)best->edx << 32)) & kvm_caps.supported_xss;
>+}
>+
> static bool kvm_cpuid_has_hyperv(struct kvm_cpuid_entry2 *entries, int nent)
> {
> struct kvm_cpuid_entry2 *entry;
>@@ -358,6 +370,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> }
>
> vcpu->arch.guest_supported_xcr0 = vcpu_get_supported_xcr0(vcpu);
>+ vcpu->arch.guest_supported_xss = vcpu_get_supported_xss(vcpu);
>
> /*
> * FP+SSE can always be saved/restored via KVM_{G,S}ET_XSAVE, even if
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 1258d1d6dd52..9a616d84bd39 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -3795,20 +3795,25 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> vcpu->arch.ia32_tsc_adjust_msr += adj;
> }
> break;
>- case MSR_IA32_XSS:
>- if (!msr_info->host_initiated &&
>- !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
>+ case MSR_IA32_XSS: {
>+ bool host_msr_reset = msr_info->host_initiated && data == 0;
>+
>+ if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES) &&
>+ (!host_msr_reset || !msr_info->host_initiated))
!msr_info->host_initiated can be dropped here.
