On Wed, 2023-01-04 at 18:02 +0000, Sean Christopherson wrote:
> On Thu, Dec 29, 2022, mlevitsk@xxxxxxxxxx wrote:
> > On Fri, 2022-12-09 at 00:00 +0200, Maxim Levitsky wrote:
> > > On Sat, 2022-10-01 at 00:59 +0000, Sean Christopherson wrote:
> > > > + } else {
> > > > + cluster = (ldr >> 4) << 2;
> > > > + if (cluster >= 0xf)
> > > > return NULL;
> > > > - } else { /* cluster */
> > > > - int cluster = (dlid & 0xf0) >> 4;
> > > > - int apic = ffs(dlid & 0x0f) - 1;
> > > > -
> > > > - if ((apic < 0) || (apic > 7) ||
> > > > - (cluster >= 0xf))
> > > > - return NULL;
> > > > - index = (cluster << 2) + apic;
> > > > + ldr &= 0xf;
> > > > }
> > > > + if (!ldr || !is_power_of_2(ldr))
> > > > + return NULL;
> > > > +
> > > > + index = __ffs(ldr);
> > > > + if (WARN_ON_ONCE(index > 7))
> > > > + return NULL;
> > > > + index += (cluster << 2);
> > > >
> > > > logical_apic_id_table = (u32 *) page_address(kvm_svm->avic_logical_id_table_page);
> > > >
> > >
> > > Looks good.
> >
> > I hate to say it but this patch has a bug:
> >
> > We have both 'cluster = (ldr >> 4) << 2' and then 'index += (cluster << 2)'
> >
> > One of the shifts has to go.
>
> The first shift is wrong. The "cluster >= 0xf" check needs to be done on the actual
> cluster. The "<< 2", a.k.a. "* 4", is specific to indexing the AVIC table.
>
> Thanks!
>
Yep, agree.
(I mean technically you can remove the second shift and do the check before doing the first shift, that
is why I told you that one of the shifts has to go)
Best regards,
Maxim Levitsky
