Re: [PATCH v6 15/17] KVM: SVM: Use target APIC ID to complete x2AVIC IRQs when possible

Suthikulpanit, Suravee
2022-06-28T02:38:06Z

On 6/28/2022 5:55 AM, Maxim Levitsky wrote:
> On Fri, 2022-06-24 at 18:41 +0200, Paolo Bonzini wrote:
>> On 5/19/22 12:27, Suravee Suthikulpanit wrote:
>>> + * If the x2APIC logical ID sub-field (i.e. icrh[15:0]) contains zero
>>> + * or more than 1 bits, we cannot match just one vcpu to kick for
>>> + * fast path.
>>> + */
>>> + if (!first || (first != last))
>>> + return -EINVAL;
>>> +
>>> + apic = first - 1;
>>> + if ((apic < 0) || (apic > 15) || (cluster >= 0xfffff))
>>> + return -EINVAL;
>>
>> Neither of these is possible: first == 0 has been cheked above, and
>> ffs(icrh & 0xffff) cannot exceed 15. Likewise, cluster is actually
>> limited to 16 bits, not 20.
>>
>> Plus, C is not Pascal so no parentheses. :)
>>
>> Putting everything together, it can be simplified to this:
>>
>> + int cluster = (icrh & 0xffff0000) >> 16;
>> + int apic = ffs(icrh & 0xffff) - 1;
>> +
>> + /*
>> + * If the x2APIC logical ID sub-field (i.e. icrh[15:0])
>> + * contains anything but a single bit, we cannot use the
>> + * fast path, because it is limited to a single vCPU.
>> + */
>> + if (apic < 0 || icrh != (1 << apic))
>> + return -EINVAL;
>> +
>> + l1_physical_id = (cluster << 4) + apic;
>>
>>
>>> + apic_id = (cluster << 4) + apic;
>
> Hi Paolo and Suravee Suthikulpanit!
>
> Note that this patch is not needed anymore, I fixed the avic_kick_target_vcpus_fast function,
> and added the support for x2apic because it was very easy to do
> (I already needed to parse logical id for flat and cluser modes)
>
> Best regards,
> Maxim Levitsky
>

Understood. I was about to send v7 to remove this patch from the series, but too late. I'll test the current queue branch and provide update.

Best Regards,
Suravee