Re: [Xen-devel] [PATCH v5 9/9] xen/x86: setup PVHv2 Dom0 ACPI tables

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.02.17 at 16:10, <roger.pau@xxxxxxxxxx> wrote:
> On Thu, Jan 26, 2017 at 07:16:32AM -0700, Jan Beulich wrote:
>> >>> On 19.01.17 at 18:29, <roger.pau@xxxxxxxxxx> wrote:
>> > +    /*
>> > +     * The APIC ID field of the local APIC struct is only 1byte, so we 
>> > need
>> > +     * to limit the number of local APIC entries to 128 because we only 
>> > use
>> > +     * even numbers as APIC IDs.
>> > +     */
>> > +    size += sizeof(*local_apic) *
>> > +            min(max_vcpus, 1U << (sizeof(local_apic->id) * 8));
>> 
>> This caps at 256 now. Perhaps it would anyway be better to use
>> HVM_MAX_VCPUS here, or maybe the minimum of both?
> 
> max_vcpus is already capped to HVM_MAX_VCPUS.

Is it? I see a use of that symbol only in mk_dsdt.c.

> IMHO it's not right to use
> HVM_MAX_VCPUS because we will increase it at some point, and then we would add
> more local APIC entries that possible thus overflowing the id field.

Hence the "or maybe the minimum of both".

>> Plus, when you cap LAPIC entries, you should also provide x2APIC
>> ones (to be able to represent all vCPU-s).
> 
> Would it make sense to then provide x2APIC entries regardless of whether they
> are present on the native tables or not?
> 
> The emulated APIC provided by Xen supports x2APIC mode anyway.

Yes, I think so.

Jan


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