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Subject: Re: [PATCH] KVM: SVM: Add a dedicated INVD intercept routine
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        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>
From:   Tom Lendacky <thomas.lendacky@amd.com>
Message-ID: <12be5ce2-2caf-ce8a-01f1-9254ca698849@amd.com>
Date:   Wed, 23 Sep 2020 15:40:00 -0500
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On 9/23/20 3:32 PM, Sean Christopherson wrote:
> On Wed, Sep 23, 2020 at 03:27:39PM -0500, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> The INVD instruction intercept performs emulation. Emulation can't be done
>> on an SEV guest because the guest memory is encrypted.
>>
>> Provide a dedicated intercept routine for the INVD intercept. Within this
>> intercept routine just skip the instruction for an SEV guest, since it is
>> emulated as a NOP anyway.
>>
>> Fixes: 1654efcbc431 ("KVM: SVM: Add KVM_SEV_INIT command")
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  arch/x86/kvm/svm/svm.c | 13 ++++++++++++-
>>  1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index c91acabf18d0..332ec4425d89 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -2183,6 +2183,17 @@ static int iret_interception(struct vcpu_svm *svm)
>>  	return 1;
>>  }
>>  
>> +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.

Thanks,
Tom

> 
>> +}
>> +
>>  static int invlpg_interception(struct vcpu_svm *svm)
>>  {
>>  	if (!static_cpu_has(X86_FEATURE_DECODEASSISTS))
>> @@ -2774,7 +2785,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
>>  	[SVM_EXIT_RDPMC]			= rdpmc_interception,
>>  	[SVM_EXIT_CPUID]			= cpuid_interception,
>>  	[SVM_EXIT_IRET]                         = iret_interception,
>> -	[SVM_EXIT_INVD]                         = emulate_on_interception,
>> +	[SVM_EXIT_INVD]                         = invd_interception,
>>  	[SVM_EXIT_PAUSE]			= pause_interception,
>>  	[SVM_EXIT_HLT]				= halt_interception,
>>  	[SVM_EXIT_INVLPG]			= invlpg_interception,
>> -- 
>> 2.28.0
>>