linux-kernel - Re: [PATCH 08/10] KVM: SVM: Mark VMCB dirty before processing incoming snp_vmsa

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Message-ID: <d9c8f6e2-36fd-7c6f-c755-e74e9d862714@amd.com>
Date: Mon, 24 Feb 2025 15:58:27 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Naveen N Rao <naveen@...nel.org>, Kim Phillips <kim.phillips@....com>,
 Alexey Kardashevskiy <aik@....com>
Subject: Re: [PATCH 08/10] KVM: SVM: Mark VMCB dirty before processing
 incoming snp_vmsa_gpa

On 2/18/25 19:27, Sean Christopherson wrote:
> Mark the VMCB dirty, i.e. zero control.clean, prior to handling the new
> VMSA.  Nothing in the VALID_PAGE() case touches control.clean, and
> isolating the VALID_PAGE() code will allow simplifying the overall logic.
> 
> Note, the VMCB probably doesn't need to be marked dirty when the VMSA is
> invalid, as KVM will disallow running the vCPU in such a state.  But it
> also doesn't hurt anything.

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/sev.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 241cf7769508..3a531232c3a1 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3852,6 +3852,12 @@ static int __sev_snp_update_protected_guest_state(struct kvm_vcpu *vcpu)
>  	/* Clear use of the VMSA */
>  	svm->vmcb->control.vmsa_pa = INVALID_PAGE;
>  
> +	/*
> +	 * When replacing the VMSA during SEV-SNP AP creation,
> +	 * mark the VMCB dirty so that full state is always reloaded.
> +	 */
> +	vmcb_mark_all_dirty(svm->vmcb);
> +
>  	if (VALID_PAGE(svm->sev_es.snp_vmsa_gpa)) {
>  		gfn_t gfn = gpa_to_gfn(svm->sev_es.snp_vmsa_gpa);
>  		struct kvm_memory_slot *slot;
> @@ -3897,12 +3903,6 @@ static int __sev_snp_update_protected_guest_state(struct kvm_vcpu *vcpu)
>  		kvm_release_page_clean(page);
>  	}
>  
> -	/*
> -	 * When replacing the VMSA during SEV-SNP AP creation,
> -	 * mark the VMCB dirty so that full state is always reloaded.
> -	 */
> -	vmcb_mark_all_dirty(svm->vmcb);
> -
>  	return 0;
>  }
>