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Subject: Re: [PATCH] KVM: SVM: Add a dedicated INVD intercept routine
To:     Tom Lendacky <thomas.lendacky@amd.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>
References: <16f36f9a51608758211c54564cd17c8b909372f1.1600892859.git.thomas.lendacky@amd.com>
 <20200923203241.GB15101@linux.intel.com>
 <12be5ce2-2caf-ce8a-01f1-9254ca698849@amd.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <d260b1e1-1a53-a7ee-e613-a806395582f6@redhat.com>
Date:   Thu, 24 Sep 2020 08:51:56 +0200
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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