Re: [PATCH 2/2] KVM: SVM: Extend host physical APIC ID field to support more than 8-bit

From: "Suthikulpanit, Suravee" <suravee.suthikulpanit@amd.com>
To: Sean Christopherson <seanjc@google.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	x86@kernel.org, pbonzini@redhat.com, joro@8bytes.org,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	peterz@infradead.org, hpa@zytor.com, thomas.lendacky@amd.com,
	jon.grimm@amd.com
Subject: Re: [PATCH 2/2] KVM: SVM: Extend host physical APIC ID field to support more than 8-bit
Date: Tue, 16 Nov 2021 02:29:46 -0800	[thread overview]
Message-ID: <34b8a586-d64e-01d0-eb95-93b7be241a4f@amd.com> (raw)
In-Reply-To: <YYwiBbyUINIcGXp3@google.com>

On 11/10/2021 11:48 AM, Sean Christopherson wrote:
>   Wed, Nov 10, 2021, Suravee Suthikulpanit wrote:
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index 989685098b3e..0b066bb5149d 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -1031,6 +1031,12 @@ static __init int svm_hardware_setup(void)
>>   			nrips = false;
>>   	}
>>   
>> +	if (avic) {
>> +		r = avic_init_host_physical_apicid_mask();
>> +		if (r)
>> +			avic = false;
>> +	}
> Haven't yet dedicated any brain cells to the rest of the patch, but this can be
> written as
> 
> 	if (avic && avic_init_host_physical_apicid_mask())
> 		avic = false;
> 
> or
> 
> 	avic = avic && !avic_init_host_physical_apicid_mask();
> 
> But looking at the context below, combining everything would be preferable.  I
> would say split out the enable_apicv part to make it more obvious that enable_apicv
> is merely a reflection of avic.
> 
> 	avic = avic && npt_enabled && boot_cpu_has(X86_FEATURE_AVIC) &&
> 	       !avic_init_host_physical_apicid_mask();
> 	enable_apicv = avic;
> 

Yes, we can do that. I'll update the logic in V2.

Thanks,
Suravee