linux-kernel - Re: [PATCH 5/9] KVM: SVM: Check for an unexpected VM-Exit after RETPOLINE "fast" handling

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Message-ID: <ouxrqqbwodwf5gne45xvrtt7t2zqrlq4lpkptwmpsilx3zndsr@yagrxfbudyjy>
Date: Fri, 14 Nov 2025 00:04:34 +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 5/9] KVM: SVM: Check for an unexpected VM-Exit after
 RETPOLINE "fast" handling

On Thu, Nov 13, 2025 at 02:56:17PM -0800, Sean Christopherson wrote:
> Check for an unexpected/unhandled VM-Exit after the manual RETPOLINE=y
> handling.  The entire point of the RETPOLINE checks is to optimize for
> common VM-Exits, i.e. checking for the rare case of an unsupported
> VM-Exit is counter-productive.  This also aligns SVM and VMX exit handling.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

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

> ---
>  arch/x86/kvm/svm/svm.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 638a67ef0c37..202a4d8088a2 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3435,12 +3435,6 @@ static void dump_vmcb(struct kvm_vcpu *vcpu)
>  
>  int svm_invoke_exit_handler(struct kvm_vcpu *vcpu, u64 exit_code)
>  {
> -	if (exit_code >= ARRAY_SIZE(svm_exit_handlers))
> -		goto unexpected_vmexit;
> -
> -	if (!svm_exit_handlers[exit_code])
> -		goto unexpected_vmexit;
> -
>  #ifdef CONFIG_MITIGATION_RETPOLINE
>  	if (exit_code == SVM_EXIT_MSR)
>  		return msr_interception(vcpu);
> @@ -3457,6 +3451,12 @@ int svm_invoke_exit_handler(struct kvm_vcpu *vcpu, u64 exit_code)
>  		return sev_handle_vmgexit(vcpu);
>  #endif
>  #endif
> +	if (exit_code >= ARRAY_SIZE(svm_exit_handlers))
> +		goto unexpected_vmexit;
> +
> +	if (!svm_exit_handlers[exit_code])
> +		goto unexpected_vmexit;
> +
>  	return svm_exit_handlers[exit_code](vcpu);
>  
>  unexpected_vmexit:
> -- 
> 2.52.0.rc1.455.g30608eb744-goog
>