linux-kernel - Re: [PATCH v11 6/8] KVM: SEV: Set RESET GHCB MSR value during sev_es_init

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Message-ID: <0f29c54c-e471-4323-ba75-2df19d67479c@amd.com>
Date: Wed, 20 Aug 2025 15:02:18 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
	<pbonzini@...hat.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Thomas Lendacky
	<thomas.lendacky@....com>, Michael Roth <michael.roth@....com>, "Borislav
 Petkov" <bp@...en8.de>, Vaishali Thakkar <vaishali.thakkar@...e.com>, "Ketan
 Chaturvedi" <Ketan.Chaturvedi@....com>, Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCH v11 6/8] KVM: SEV: Set RESET GHCB MSR value during
 sev_es_init_vmcb()



On 8/20/2025 5:18 AM, Sean Christopherson wrote:
> Set the RESET value for the GHCB "MSR" during sev_es_init_vmcb() instead
> of sev_es_vcpu_reset() to allow for dropping sev_es_vcpu_reset() entirely.
> 
> Note, the call to sev_init_vmcb() from sev_migrate_from() also kinda sorta
> emulates a RESET, but sev_migrate_from() immediate overwrites ghcb_gpa

s/immediate/immediately/

> with the source's current value, so whether or not stuffing the GHCB
> version is correct/desirable is moot.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Nikunj A Dadhania <nikunj@....com>

> ---
>  arch/x86/kvm/svm/sev.c | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c5726b091680..ee7a05843548 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -4480,7 +4480,7 @@ void sev_vcpu_after_set_cpuid(struct vcpu_svm *svm)
>  		vcpu->arch.reserved_gpa_bits &= ~(1UL << (best->ebx & 0x3f));
>  }
>  
> -static void sev_es_init_vmcb(struct vcpu_svm *svm)
> +static void sev_es_init_vmcb(struct vcpu_svm *svm, bool init_event)
>  {
>  	struct kvm_sev_info *sev = to_kvm_sev_info(svm->vcpu.kvm);
>  	struct vmcb *vmcb = svm->vmcb01.ptr;
> @@ -4541,6 +4541,15 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
>  
>  	/* Can't intercept XSETBV, HV can't modify XCR0 directly */
>  	svm_clr_intercept(svm, INTERCEPT_XSETBV);
> +
> +	/*
> +	 * Set the GHCB MSR value as per the GHCB specification when emulating
> +	 * vCPU RESET for an SEV-ES guest.
> +	 */
> +	if (!init_event)
> +		set_ghcb_msr(svm, GHCB_MSR_SEV_INFO((__u64)sev->ghcb_version,
> +						    GHCB_VERSION_MIN,
> +						    sev_enc_bit));
>  }
>  
>  void sev_init_vmcb(struct vcpu_svm *svm, bool init_event)
> @@ -4560,7 +4569,7 @@ void sev_init_vmcb(struct vcpu_svm *svm, bool init_event)
>  		sev_snp_init_protected_guest_state(vcpu);
>  
>  	if (sev_es_guest(vcpu->kvm))
> -		sev_es_init_vmcb(svm);
> +		sev_es_init_vmcb(svm, init_event);
>  }
>  
>  int sev_vcpu_create(struct kvm_vcpu *vcpu)
> @@ -4585,17 +4594,6 @@ int sev_vcpu_create(struct kvm_vcpu *vcpu)
>  
>  void sev_es_vcpu_reset(struct vcpu_svm *svm)
>  {
> -	struct kvm_vcpu *vcpu = &svm->vcpu;
> -	struct kvm_sev_info *sev = to_kvm_sev_info(vcpu->kvm);
> -
> -	/*
> -	 * Set the GHCB MSR value as per the GHCB specification when emulating
> -	 * vCPU RESET for an SEV-ES guest.
> -	 */
> -	set_ghcb_msr(svm, GHCB_MSR_SEV_INFO((__u64)sev->ghcb_version,
> -					    GHCB_VERSION_MIN,
> -					    sev_enc_bit));
> -
>  	mutex_init(&svm->sev_es.snp_vmsa_mutex);
>  }
>