linux-kernel - Re: [PATCH v6 3/9] KVM: x86: Stuff vCPU's PAT with default value at RESET, not creation

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Message-ID: <b0a3ebe8-c69e-47f7-9dcd-021d60c36111@intel.com>
Date: Mon, 1 Apr 2024 14:00:20 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 Shan Kang <shan.kang@...el.com>, Kai Huang <kai.huang@...el.com>,
 Xin Li <xin3.li@...el.com>
Subject: Re: [PATCH v6 3/9] KVM: x86: Stuff vCPU's PAT with default value at
 RESET, not creation

On 3/9/2024 9:27 AM, Sean Christopherson wrote:
> Move the stuffing of the vCPU's PAT to the architectural "default" value
> from kvm_arch_vcpu_create() to kvm_vcpu_reset(), guarded by !init_event,
> to better capture that the default value is the value "Following Power-up
> or Reset".  E.g. setting PAT only during creation would break if KVM were
> to expose a RESET ioctl() to userspace (which is unlikely, but that's not
> a good reason to have unintuitive code).
> 
> No functional change.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

> ---
>   arch/x86/kvm/x86.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 66c4381460dc..eac97b1b8379 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12134,8 +12134,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>   	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>   	vcpu->arch.reserved_gpa_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu);
>   
> -	vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;
> -
>   	kvm_async_pf_hash_reset(vcpu);
>   
>   	vcpu->arch.perf_capabilities = kvm_caps.supported_perf_cap;
> @@ -12302,6 +12300,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	if (!init_event) {
>   		vcpu->arch.smbase = 0x30000;
>   
> +		vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;
> +
>   		vcpu->arch.msr_misc_features_enables = 0;
>   		vcpu->arch.ia32_misc_enable_msr = MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL |
>   						  MSR_IA32_MISC_ENABLE_BTS_UNAVAIL;