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Date:   Thu, 20 Jan 2022 15:44:04 +0000
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Subject: Re: [PATCH 6/9] KVM: SVM: WARN if KVM attempts emulation on #UD or
 #GP for SEV guests
Content-Language: en-GB
To:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Liam Merwick <liam.merwick@oracle.com>
References: <20220120010719.711476-1-seanjc@google.com>
 <20220120010719.711476-7-seanjc@google.com>
From:   Liam Merwick <liam.merwick@oracle.com>
In-Reply-To: <20220120010719.711476-7-seanjc@google.com>
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On 20/01/2022 01:07, Sean Christopherson wrote:
> WARN if KVM attempts to emulate in response to #UD or #GP for SEV guests,
> i.e. if KVM intercepts #UD or #GP, as emulation on any fault except #NPF
> is impossible since KVM cannot read guest private memory to get the code
> stream, and the CPU's DecodeAssists feature only provides the instruction
> bytes on #NPF.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/kvm/svm/svm.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 994224ae2731..ed2ca875b84b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4267,6 +4267,9 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
>   	if (!sev_guest(vcpu->kvm))
>   		return true;
>   
> +	/* #UD and #GP should never be intercepted for SEV guests. */
> +	WARN_ON_ONCE(emul_type & (EMULTYPE_TRAP_UD | EMULTYPE_VMWARE_GP));

What about EMULTYPE_TRAP_UD_FORCED?

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


> +
>   	/*
>   	 * Emulation is impossible for SEV-ES guests as KVM doesn't have access
>   	 * to guest register state.