linux-kernel - Re: [PATCH] KVM: SEV: Save the SEV policy if and only if LAUNCH

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Message-ID: <32c3a25d-8e5a-0f81-8cb2-655dd39f98ba@amd.com>
Date: Thu, 21 Aug 2025 17:18:55 -0500
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,
 Kim Phillips <kim.phillips@....com>
Subject: Re: [PATCH] KVM: SEV: Save the SEV policy if and only if LAUNCH_START
 succeeds

On 8/21/25 16:38, Sean Christopherson wrote:
> Wait until LAUNCH_START fully succeeds to set a VM's SEV/SNP policy so
> that KVM doesn't keep a potentially stale policy.  In practice, the issue
> is benign as the policy is only used to detect if the VMSA can be
> decrypted, and the VMSA only needs to be decrypted if LAUNCH_UPDATE and
> thus LAUNCH_START succeeded.
> 
> Fixes: 962e2b6152ef ("KVM: SVM: Decrypt SEV VMSA in dump_vmcb() if debugging is enabled")
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Kim Phillips <kim.phillips@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

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

> ---
>  arch/x86/kvm/svm/sev.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index f4381878a9e5..65b59939754c 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -583,8 +583,6 @@ static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	if (copy_from_user(&params, u64_to_user_ptr(argp->data), sizeof(params)))
>  		return -EFAULT;
>  
> -	sev->policy = params.policy;
> -
>  	memset(&start, 0, sizeof(start));
>  
>  	dh_blob = NULL;
> @@ -632,6 +630,7 @@ static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		goto e_free_session;
>  	}
>  
> +	sev->policy = params.policy;
>  	sev->handle = start.handle;
>  	sev->fd = argp->sev_fd;
>  
> @@ -2201,8 +2200,6 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		start.desired_tsc_khz = kvm->arch.default_tsc_khz;
>  	}
>  
> -	sev->policy = params.policy;
> -
>  	sev->snp_context = snp_context_create(kvm, argp);
>  	if (!sev->snp_context)
>  		return -ENOTTY;
> @@ -2218,6 +2215,7 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		goto e_free_context;
>  	}
>  
> +	sev->policy = params.policy;
>  	sev->fd = argp->sev_fd;
>  	rc = snp_bind_asid(kvm, &argp->error);
>  	if (rc) {
> 
> base-commit: ecbcc2461839e848970468b44db32282e5059925