Re: [PATCH v3 3/3] KVM: SVM: Extend host physical APIC ID field to support more than 8-bit

[Suthikulpanit, Suravee]

Sean,

On 12/31/2021 12:21 AM, Sean Christopherson wrote:
> On Mon, Dec 13, 2021, Suravee Suthikulpanit wrote:
> > The AVIC physical APIC ID table entry contains the host physical
> > APIC ID field, which the hardware uses to keep track of where each
> > vCPU is running. Originally, the field is an 8-bit value, which can
> > only support physical APIC ID up to 255.
> >
> > To support system with larger APIC ID, the AVIC hardware extends
> > this field to support up to the largest possible physical APIC ID
> > available on the system.
> >
> > Therefore, replace the hard-coded mask value with the value
> > calculated from the maximum possible physical APIC ID in the system.
>
> ...
>
> > +static void avic_init_host_physical_apicid_mask(void)
> > +{
> > +	if (!x2apic_mode) {
> > +		/* If host is in xAPIC mode, default to only 8-bit mask. */
> > +		avic_host_physical_id_mask = 0xffULL;
>
> Use GENMASK(7:0) instead of open coding the equivalent.  Oh, and
> avic_host_physical_id_mask doesn't need to be a u64, it's hard capped at 12 bits
> and so can be a simple int.

Actually, shouldn't it be u16 since the value returned from kvm_cpu_get_apicid()
would typically be 16-bit value (despite it has int as a return type).

Regards,
Suravee