linux-kernel - Re: [PATCH v2 02/21] KVM: x86: Add a helper to query whether or not a vCPU has ever run

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Date:   Tue, 14 Feb 2023 14:35:48 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Like Xu <like.xu.linux@...il.com>
Subject: Re: [PATCH v2 02/21] KVM: x86: Add a helper to query whether or not a
 vCPU has ever run

On 2/10/2023 8:31 AM, Sean Christopherson wrote:
> Add a helper to query if a vCPU has run so that KVM doesn't have to open
> code the check on last_vmentry_cpu being set to a magic value.
> 
> No functional change intended.
> 
> Suggested-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Cc: Like Xu <like.xu.linux@...il.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

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

> ---
>   arch/x86/kvm/cpuid.c   | 2 +-
>   arch/x86/kvm/mmu/mmu.c | 2 +-
>   arch/x86/kvm/x86.h     | 5 +++++
>   3 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8f8edeaf8177..448d627ce891 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -420,7 +420,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
>   	 * KVM_SET_CPUID{,2} again. To support this legacy behavior, check
>   	 * whether the supplied CPUID data is equal to what's already set.
>   	 */
> -	if (vcpu->arch.last_vmentry_cpu != -1) {
> +	if (kvm_vcpu_has_run(vcpu)) {
>   		r = kvm_cpuid_check_equal(vcpu, e2, nent);
>   		if (r)
>   			return r;
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index c91ee2927dd7..b0693195273b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5393,7 +5393,7 @@ void kvm_mmu_after_set_cpuid(struct kvm_vcpu *vcpu)
>   	 * Changing guest CPUID after KVM_RUN is forbidden, see the comment in
>   	 * kvm_arch_vcpu_ioctl().
>   	 */
> -	KVM_BUG_ON(vcpu->arch.last_vmentry_cpu != -1, vcpu->kvm);
> +	KVM_BUG_ON(kvm_vcpu_has_run(vcpu), vcpu->kvm);
>   }
>   
>   void kvm_mmu_reset_context(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index a8167b47b8c8..754190af1791 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -83,6 +83,11 @@ static inline unsigned int __shrink_ple_window(unsigned int val,
>   void kvm_service_local_tlb_flush_requests(struct kvm_vcpu *vcpu);
>   int kvm_check_nested_events(struct kvm_vcpu *vcpu);
>   
> +static inline bool kvm_vcpu_has_run(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.last_vmentry_cpu != -1;
> +}
> +
>   static inline bool kvm_is_exception_pending(struct kvm_vcpu *vcpu)
>   {
>   	return vcpu->arch.exception.pending ||