linux-kernel - Re: [PATCH v2 8/8] KVM: SVM: Assert that Hyper-V's HV_SVM_EXITCODE_ENL == SVM_EXIT

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Message-ID: <87eco8bajg.fsf@redhat.com>
Date: Fri, 02 Jan 2026 10:58:59 +0100
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>, "K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang
 Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, Dexuan Cui
 <decui@...rosoft.com>, Long Li <longli@...rosoft.com>
Cc: kvm@...r.kernel.org, linux-hyperv@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>, Yosry
 Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH v2 8/8] KVM: SVM: Assert that Hyper-V's
 HV_SVM_EXITCODE_ENL == SVM_EXIT_SW

Sean Christopherson <seanjc@...gle.com> writes:

> Add a build-time assertiont that Hyper-V's "enlightened" exit code is that,
> same as the AMD-defined "Reserved for Host" exit code, mostly to help
> readers connect the dots and understand why synthesizing a software-defined
> exit code is safe/ok.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/hyperv.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/hyperv.c b/arch/x86/kvm/svm/hyperv.c
> index 3ec580d687f5..4f24dcb45116 100644
> --- a/arch/x86/kvm/svm/hyperv.c
> +++ b/arch/x86/kvm/svm/hyperv.c
> @@ -10,6 +10,12 @@ void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  
> +	/*
> +	 * The exit code used by Hyper-V for software-defined exits is reserved
> +	 * by AMD specifically for such use cases.
> +	 */
> +	BUILD_BUG_ON(HV_SVM_EXITCODE_ENL != SVM_EXIT_SW);
> +
>  	svm->vmcb->control.exit_code = HV_SVM_EXITCODE_ENL;
>  	svm->vmcb->control.exit_info_1 = HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH;
>  	svm->vmcb->control.exit_info_2 = 0;

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

Alternatively (or additionally?) to BUG_ON, I guess we could've

#define HV_SVM_EXITCODE_ENL SVM_EXIT_SW 

unless including SVM's headers into include/hyperv/hvgdk.h is too big of
a mess.

-- 
Vitaly