Re: [PATCH 6/9] KVM: SVM: WARN if KVM attempts emulation on #UD or #GP for SEV guests

From: Liam Merwick <liam.merwick@oracle.com>
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>
Subject: Re: [PATCH 6/9] KVM: SVM: WARN if KVM attempts emulation on #UD or #GP for SEV guests
Date: Thu, 20 Jan 2022 15:44:04 +0000	[thread overview]
Message-ID: <483ed34e-3125-7efb-1178-22f02173667a@oracle.com> (raw)
In-Reply-To: <20220120010719.711476-7-seanjc@google.com>

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.