linux-kernel - Re: [PATCH v6 12/25] KVM: x86: Refresh CPUID on write to guest MSR_IA32

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Date:   Sun, 8 Oct 2023 13:54:49 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dave.hansen@...el.com>,
        <peterz@...radead.org>, <rick.p.edgecombe@...el.com>,
        <john.allen@....com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v6 12/25] KVM: x86: Refresh CPUID on write to guest
 MSR_IA32_XSS

>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.