linux-kernel - Re: [PATCH v5 12/34] KVM: SVM: Add initial support for a VMGEXIT VMEXIT

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Message-ID: <X9fAAhF2LzOmZAtv@google.com>
Date:   Mon, 14 Dec 2020 11:41:54 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v5 12/34] KVM: SVM: Add initial support for a VMGEXIT
 VMEXIT

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.