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Message-ID: <85f9bf76-05ec-8948-4ef1-42a57d641766@linux.intel.com>
Date: Mon, 24 Apr 2023 09:38:59 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
pbonzini@...hat.com, peterz@...radead.org, john.allen@....com,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: rick.p.edgecombe@...el.com, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v2 07/21] KVM:x86: Refresh CPUID on write to guest
MSR_IA32_XSS
On 4/21/2023 9:46 PM, Yang Weijiang wrote:
> Update CPUID(EAX=0DH,ECX=1) when the guest's XSS is modified.
> CPUID(EAX=0DH,ECX=1).EBX reports current required storage size for all
> features enabled via XCR0 | XSS so that guest can allocate correct xsave
> buffer.
>
> Note, KVM does not yet support any XSS based features, i.e. supported_xss
> is guaranteed to be zero at this time.
>
> Co-developed-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
> arch/x86/kvm/cpuid.c | 11 ++++++++---
> arch/x86/kvm/x86.c | 6 ++++--
> 2 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 123bf8b97a4b..dd6d5150d86a 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -276,9 +276,14 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e
> best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
>
> 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);
> + if (best) {
> + if (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
> + cpuid_entry_has(best, X86_FEATURE_XSAVEC)) {
Is it necessary to change to use two ifs?
> + u64 xstate = vcpu->arch.xcr0 | vcpu->arch.ia32_xss;
> +
> + best->ebx = xstate_required_size(xstate, true);
> + }
> + }
>
> best = __kvm_find_kvm_cpuid_features(vcpu, entries, nent);
> if (kvm_hlt_in_guest(vcpu->kvm) && best &&
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 33a780fe820b..ab3360a10933 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3776,8 +3776,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> */
> if (data & ~kvm_caps.supported_xss)
> return 1;
> - vcpu->arch.ia32_xss = data;
> - kvm_update_cpuid_runtime(vcpu);
> + if (vcpu->arch.ia32_xss != data) {
> + vcpu->arch.ia32_xss = data;
> + kvm_update_cpuid_runtime(vcpu);
> + }
> break;
> case MSR_SMI_COUNT:
> if (!msr_info->host_initiated)
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