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Date:   Mon, 14 Dec 2020 11:41:54 -0800
From:   Sean Christopherson <seanjc@google.com>
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [PATCH v5 12/34] KVM: SVM: Add initial support for a VMGEXIT
 VMEXIT
Message-ID: <X9fAAhF2LzOmZAtv@google.com>
References: <cover.1607620209.git.thomas.lendacky@amd.com>
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 <7bac31c8-a008-8223-0ed5-9c25012e380a@redhat.com>
 <33e98d2d-93b5-acd6-4608-f30c709019ad@amd.com>
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On Mon, Dec 14, 2020, Tom Lendacky wrote:
> On 12/14/20 9:45 AM, Paolo Bonzini wrote:
> > On 10/12/20 18:09, Tom Lendacky wrote:
> >> @@ -3184,6 +3186,8 @@ static int svm_invoke_exit_handler(struct vcpu_svm
> >> *svm, u64 exit_code)
> >> ????????? return halt_interception(svm);
> >> ????? else if (exit_code == SVM_EXIT_NPF)
> >> ????????? return npf_interception(svm);
> >> +??? else if (exit_code == SVM_EXIT_VMGEXIT)
> >> +??????? return sev_handle_vmgexit(svm);
> > 
> > Are these common enough to warrant putting them in this short list?
> 
> A VMGEXIT exit occurs for any of the listed NAE events in the GHCB
> specification (e.g. CPUID, RDMSR/WRMSR, MMIO, port IO, etc.) if those
> events are being intercepted (or triggered in the case of MMIO). It will
> depend on what is considered common. Since SVM_EXIT_MSR was already in the
> list, I figured I should add VMGEXIT.

I agree VMGEXIT should be added to the hot path, it could very well be the most
common exit reason due to all instruction-based emulation getting funneled
through VMGEXIT.