linux-kernel - Re: [PATCH 1/9] KVM: nSVM: Clear exit_code_hi in VMCB when synthesizing nested VM-Exits

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Message-ID: <2fd7bzpxany4ymoqlqlkrtapaxbhnv7xs6nd7hwqnkskyr5jdh@bscvvwnoj7zj>
Date: Thu, 13 Nov 2025 23:03:56 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>, "K. Y. Srinivasan" <kys@...rosoft.com>, 
	Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, 
	kvm@...r.kernel.org, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH 1/9] KVM: nSVM: Clear exit_code_hi in VMCB when
 synthesizing nested VM-Exits

On Thu, Nov 13, 2025 at 02:56:13PM -0800, Sean Christopherson wrote:
> Explicitly clear exit_code_hi in the VMCB when synthesizing "normal"
> nested VM-Exits, as the full exit code is a 64-bit value (spoiler alert),
> and all exit codes for non-failing VMRUN use only bits 31:0.
> 
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Yosry Ahmed <yosry.ahmed@...ux.dev>

> ---
>  arch/x86/kvm/svm/svm.c | 2 ++
>  arch/x86/kvm/svm/svm.h | 7 ++++---
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index fc42bcdbb520..7ea034ee6b6c 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2433,6 +2433,7 @@ static bool check_selective_cr0_intercepted(struct kvm_vcpu *vcpu,
>  
>  	if (cr0 ^ val) {
>  		svm->vmcb->control.exit_code = SVM_EXIT_CR0_SEL_WRITE;
> +		svm->vmcb->control.exit_code_hi = 0;
>  		ret = (nested_svm_exit_handled(svm) == NESTED_EXIT_DONE);
>  	}
>  
> @@ -4608,6 +4609,7 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
>  	if (static_cpu_has(X86_FEATURE_NRIPS))
>  		vmcb->control.next_rip  = info->next_rip;
>  	vmcb->control.exit_code = icpt_info.exit_code;
> +	vmcb->control.exit_code_hi = 0;
>  	vmexit = nested_svm_exit_handled(svm);
>  
>  	ret = (vmexit == NESTED_EXIT_DONE) ? X86EMUL_INTERCEPTED
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index c2acaa49ee1c..253a8dca412c 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -763,9 +763,10 @@ int nested_svm_vmexit(struct vcpu_svm *svm);
>  
>  static inline int nested_svm_simple_vmexit(struct vcpu_svm *svm, u32 exit_code)
>  {
> -	svm->vmcb->control.exit_code   = exit_code;
> -	svm->vmcb->control.exit_info_1 = 0;
> -	svm->vmcb->control.exit_info_2 = 0;
> +	svm->vmcb->control.exit_code	= exit_code;
> +	svm->vmcb->control.exit_code_hi	= 0;
> +	svm->vmcb->control.exit_info_1	= 0;
> +	svm->vmcb->control.exit_info_2	= 0;
>  	return nested_svm_vmexit(svm);
>  }
>  
> -- 
> 2.52.0.rc1.455.g30608eb744-goog
>