linux-kernel - Re: [PATCH v2 7/9] KVM: x86: allow L1 to not intercept triple fault

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Date:   Mon, 21 Nov 2022 16:33:41 +0000
From:   Liam Merwick <liam.merwick@...cle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Chenyi Qiang <chenyi.qiang@...el.com>,
        Yang Zhong <yang.zhong@...el.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        Borislav Petkov <bp@...en8.de>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kselftest@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Wei Wang <wei.w.wang@...el.com>,
        David Matlack <dmatlack@...gle.com>,
        Liam Merwick <liam.merwick@...cle.com>
Subject: Re: [PATCH v2 7/9] KVM: x86: allow L1 to not intercept triple fault

On 03/11/2022 14:13, Maxim Levitsky wrote:
> This is SVM correctness fix - although a sane L1 would intercept
> SHUTDOWN event, it doesn't have to, so we have to honour this.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>   arch/x86/kvm/svm/nested.c |  6 ++++++
>   arch/x86/kvm/vmx/nested.c |  1 +
>   arch/x86/kvm/x86.c        | 11 ++++++-----
>   3 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index bcc4f6620f8aec..3aa9184d1e4ed7 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1092,6 +1092,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>   
>   static void nested_svm_triple_fault(struct kvm_vcpu *vcpu)
>   {
> +	struct vcpu_svm *svm = to_svm(vcpu);
> +
> +	if (!vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_SHUTDOWN))
> +		return;
> +
> +	kvm_clear_request(KVM_REQ_TRIPLE_FAULT, vcpu);
>   	nested_svm_simple_vmexit(to_svm(vcpu), SVM_EXIT_SHUTDOWN);

You could replace 'to_svm(vcpu)' with 'svm' here
But LGTM either way.

Reviewed-by: Liam Merwick <liam.merwick@...cle.com>


>   }
>   
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 1ebe141a0a015f..7924dea9367813 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4855,6 +4855,7 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
>   
>   static void nested_vmx_triple_fault(struct kvm_vcpu *vcpu)
>   {
> +	kvm_clear_request(KVM_REQ_TRIPLE_FAULT, vcpu);
>   	nested_vmx_vmexit(vcpu, EXIT_REASON_TRIPLE_FAULT, 0, 0);
>   }
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3fd900504e683b..f0a0102a78f5c3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9741,7 +9741,7 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu)
>   
>   int kvm_check_nested_events(struct kvm_vcpu *vcpu)
>   {
> -	if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
> +	if (kvm_test_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
>   		kvm_x86_ops.nested_ops->triple_fault(vcpu);
>   		return 1;
>   	}
> @@ -10255,15 +10255,16 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   			r = 0;
>   			goto out;
>   		}
> -		if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
> -			if (is_guest_mode(vcpu)) {
> +		if (kvm_test_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
> +			if (is_guest_mode(vcpu))
>   				kvm_x86_ops.nested_ops->triple_fault(vcpu);
> -			} else {
> +
> +			if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
>   				vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
>   				vcpu->mmio_needed = 0;
>   				r = 0;
> -				goto out;
>   			}
> +			goto out;
>   		}
>   		if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
>   			/* Page is swapped out. Do synthetic halt */