linux-kernel - Re: [PATCH 2/2] KVM: SVM: Initialize vmsa_pa in VMCB to INVALID

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Message-ID: <18b86c31-e657-42e7-bca6-ddae52ead231@oracle.com>
Date: Wed, 4 Jun 2025 12:15:28 +0100
From: Liam Merwick <liam.merwick@...cle.com>
To: Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        James Houghton <jthoughton@...gle.com>,
        Peter Gonda <pgonda@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 2/2] KVM: SVM: Initialize vmsa_pa in VMCB to INVALID_PAGE
 if VMSA page is NULL



On 02/06/2025 23:44, Sean Christopherson wrote:
> When creating an SEV-ES vCPU for intra-host migration, set its vmsa_pa to
> INVALID_PAGE to harden against doing VMRUN with a bogus VMSA (KVM checks
> for a valid VMSA page in pre_sev_run()).
> 
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Liam Merwick <liam.merwick@...cle.com>
Tested-by: Liam Merwick <liam.merwick@...cle.com>


> ---
>   arch/x86/kvm/svm/sev.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 93d899454535..5ebb265f2075 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -4471,8 +4471,12 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
>   	 * the VMSA will be NULL if this vCPU is the destination for intrahost
>   	 * migration, and will be copied later.
>   	 */
> -	if (svm->sev_es.vmsa && !svm->sev_es.snp_has_guest_vmsa)
> -		svm->vmcb->control.vmsa_pa = __pa(svm->sev_es.vmsa);
> +	if (!svm->sev_es.snp_has_guest_vmsa) {
> +		if (svm->sev_es.vmsa)
> +			svm->vmcb->control.vmsa_pa = __pa(svm->sev_es.vmsa);
> +		else
> +			svm->vmcb->control.vmsa_pa = INVALID_PAGE;
> +	}
>   
>   	/* Can't intercept CR register access, HV can't modify CR registers */
>   	svm_clr_intercept(svm, INTERCEPT_CR0_READ);