Re: [Qemu-devel] [for-2.1 PATCH v2 2/2] i386/acpi-build: support hotplug of VCPU with APIC ID 0xFF

[Laszlo Ersek <lersek@redhat.com>]

On 03/18/14 15:54, Eduardo Habkost wrote:
> On Tue, Mar 18, 2014 at 04:03:25PM +0200, Michael S. Tsirkin wrote:
>> On Mon, Mar 17, 2014 at 05:05:17PM +0100, Laszlo Ersek wrote:
>>> Building on the previous patch, raise the maximal count of processor
>>> objects / NTFY branches / CPON elements from 255 to 256. This allows the
>>> VCPU with APIC ID 0xFF to be hotplugged.
>>>
>>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>>
>>
>> I note that we still have:
>>     if (endvalue >= MAX_CPUMASK_BITS) {
>>         endvalue = MAX_CPUMASK_BITS - 1;
>>         fprintf(stderr,
>>             "qemu: NUMA: A max of %d VCPUs are supported\n",
>>              MAX_CPUMASK_BITS);
>>     }
>> and MAX_CPUMASK_BITS is 255.
>>
>> Seems inconsistent?
>>
> 
> MAX_CPUMASK_BITS (now renamed to MAX_CPUS) limits CPU indexes and total
> CPU count. This patch is about APIC IDs (which may be larger than
> max_cpus if threads-per-core or cores-per-socket is not a power of 2).

Yea I welcome Eduardo's patchset not only because it fixes the
out-of-range accesses caused by "uncontrolled" APIC IDs, but also
because it disentangles these limits from one another.

Thanks
Laszlo