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

[Suthikulpanit, Suravee]

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