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Re: [PATCH v7 04/10] tools/hvmloader: Retrieve (x2)APIC IDs from the APs themselves
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 30 Oct 2024 13:04:21 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 30 Oct 2024 12:04:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.10.2024 12:31, Andrew Cooper wrote:
> On 21/10/2024 4:45 pm, Alejandro Vallejo wrote:
>> --- a/tools/firmware/hvmloader/mp_tables.c
>> +++ b/tools/firmware/hvmloader/mp_tables.c
>> @@ -198,8 +198,10 @@ static void fill_mp_config_table(struct mp_config_table
>> *mpct, int length)
>> /* fills in an MP processor entry for VCPU 'vcpu_id' */
>> static void fill_mp_proc_entry(struct mp_proc_entry *mppe, int vcpu_id)
>> {
>> + ASSERT(cpu_to_x2apicid[vcpu_id] < 0xFF );
>
> This is just going to break when we hit 256 vCPUs in a VM.
>
> What do real systems do?
>
> They'll either wrap around 255 like the CPUID xAPIC_ID does, or they'll
> not write out MP tables at all.
"at all" may be going a little far. They may simply not advertise CPUs with
too wide APIC IDs there, while still allowing others to be discovered this
legacy way.
Jan
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