linux-kernel - Re: [PATCH] KVM: SVM: Add a dedicated INVD intercept routine

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Date:   Thu, 24 Sep 2020 08:51:56 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] KVM: SVM: Add a dedicated INVD intercept routine

On 23/09/20 22:40, Tom Lendacky wrote:
>>> +static int invd_interception(struct vcpu_svm *svm)
>>> +{
>>> +	/*
>>> +	 * Can't do emulation on an SEV guest and INVD is emulated
>>> +	 * as a NOP, so just skip the instruction.
>>> +	 */
>>> +	return (sev_guest(svm->vcpu.kvm))
>>> +		? kvm_skip_emulated_instruction(&svm->vcpu)
>>> +		: kvm_emulate_instruction(&svm->vcpu, 0);
>>
>> Is there any reason not to do kvm_skip_emulated_instruction() for both SEV
>> and legacy?  VMX has the same odd kvm_emulate_instruction() call, but AFAICT
>> that's completely unecessary, i.e. VMX can also convert to a straight skip.
> 
> You could, I just figured I'd leave the legacy behavior just in case. Not
> that I can think of a reason that behavior would ever change.

Yeah, let's do skip for both SVM and VMX.

Paolo