linux-kernel - Re: [PATCH] KVM: x86: Add a helper to dedup reporting of unhandled VM-Exits

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Message-ID: <bophxumzbp2yuovzhvt62jeb5e6vwc2mirvcl6uyztse5mqvjt@xmbhgmqnpn5d>
Date: Fri, 31 Oct 2025 13:44:11 +0800
From: Yao Yuan <yaoyuan@...ux.alibaba.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Add a helper to dedup reporting of unhandled
 VM-Exits

On Thu, Oct 30, 2025 at 11:50:03AM +0800, Sean Christopherson wrote:
> Add and use a helper, kvm_prepare_unexpected_reason_exit(), to dedup the
> code that fills the exit reason and CPU when KVM encounters a VM-Exit that
> KVM doesn't know how to handle.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/svm/svm.c          |  7 +------
>  arch/x86/kvm/vmx/tdx.c          |  6 +-----
>  arch/x86/kvm/vmx/vmx.c          |  9 +--------
>  arch/x86/kvm/x86.c              | 12 ++++++++++++
>  5 files changed, 16 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 48598d017d6f..4fbe4b7ce1da 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -2167,6 +2167,7 @@ void __kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu,
>  void kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu);
>
>  void kvm_prepare_event_vectoring_exit(struct kvm_vcpu *vcpu, gpa_t gpa);
> +void kvm_prepare_unexpected_reason_exit(struct kvm_vcpu *vcpu, u64 exit_reason);
>
>  void kvm_enable_efer_bits(u64);
>  bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index f14709a511aa..83e0d4d5f4c5 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3451,13 +3451,8 @@ static bool svm_check_exit_valid(u64 exit_code)
>
>  static int svm_handle_invalid_exit(struct kvm_vcpu *vcpu, u64 exit_code)
>  {
> -	vcpu_unimpl(vcpu, "svm: unexpected exit reason 0x%llx\n", exit_code);
>  	dump_vmcb(vcpu);
> -	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> -	vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
> -	vcpu->run->internal.ndata = 2;
> -	vcpu->run->internal.data[0] = exit_code;
> -	vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
> +	kvm_prepare_unexpected_reason_exit(vcpu, exit_code);
>  	return 0;
>  }
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 326db9b9c567..079d9f13eddb 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -2145,11 +2145,7 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
>  	}
>
>  unhandled_exit:
> -	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> -	vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
> -	vcpu->run->internal.ndata = 2;
> -	vcpu->run->internal.data[0] = vp_enter_ret;
> -	vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
> +	kvm_prepare_unexpected_reason_exit(vcpu, vp_enter_ret);
>  	return 0;
>  }
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 1021d3b65ea0..08f7957ed4c3 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6642,15 +6642,8 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>  	return kvm_vmx_exit_handlers[exit_handler_index](vcpu);
>
>  unexpected_vmexit:
> -	vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
> -		    exit_reason.full);
>  	dump_vmcs(vcpu);
> -	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> -	vcpu->run->internal.suberror =
> -			KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
> -	vcpu->run->internal.ndata = 2;
> -	vcpu->run->internal.data[0] = exit_reason.full;
> -	vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
> +	kvm_prepare_unexpected_reason_exit(vcpu, exit_reason.full);
>  	return 0;
>  }
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b4b5d2d09634..c826cd05228a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9110,6 +9110,18 @@ void kvm_prepare_event_vectoring_exit(struct kvm_vcpu *vcpu, gpa_t gpa)
>  }
>  EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_prepare_event_vectoring_exit);
>
> +void kvm_prepare_unexpected_reason_exit(struct kvm_vcpu *vcpu, u64 exit_reason)
> +{
> +	vcpu_unimpl(vcpu, "unexpected exit reason 0x%llx\n", exit_reason);

I like the dedup, and this brings above for tdx which not
before. Just one small thing: Will it be better if keep the
"vmx"/"svm" hint as before and plus the "tdx" hint yet ?

Reviewed-by: Yao Yuan <yaoyuan@...ux.alibaba.com>

> +
> +	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> +	vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
> +	vcpu->run->internal.ndata = 2;
> +	vcpu->run->internal.data[0] = exit_reason;
> +	vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
> +}
> +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_prepare_unexpected_reason_exit);
> +
>  static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
>  {
>  	struct kvm *kvm = vcpu->kvm;
>
> base-commit: 4cc167c50eb19d44ac7e204938724e685e3d8057
> --
> 2.51.1.930.gacf6e81ea2-goog
>