Re: [PATCH v6 12/25] KVM: x86: Refresh CPUID on write to guest MSR_IA32_XSS

["Yang, Weijiang" <weijiang.yang@intel.com>]

On 10/8/2023 1:54 PM, Chao Gao wrote:
>> 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?

OK, will do it, thanks!

>> 	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.

Yes, it's not necessary, will remove it, thanks!