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Re: [PATCH v3 2/2] xen/x86: Change stub page allocation/free
- To: Jason Andryuk <jason.andryuk@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 11 Jun 2026 17:10:05 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 11 Jun 2026 15:10:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10.06.2026 17:23, Jason Andryuk wrote:
> On 2026-06-10 11:01, Roger Pau Monné wrote:
>> On Mon, Jun 08, 2026 at 08:06:38PM -0400, Jason Andryuk wrote:
>>> --- a/xen/arch/x86/setup.c
>>> +++ b/xen/arch/x86/setup.c
>>> @@ -2089,8 +2089,7 @@ void asmlinkage __init noreturn __start_xen(void)
>>> init_idle_domain();
>>> - this_cpu(stubs.addr) = alloc_stub_page(smp_processor_id(),
>>> - &this_cpu(stubs).mfn);
>>> + this_cpu(stubs.addr) = assign_stub_page(0);
>>
>> Given stub pages is first used quite late in the boot process, the above
>> arrays would better be dynamically allocated using xvmalloc_array().
>
> Ok. At some point I intended to dynamically allocate. But x86 doesn't have
> num_possible_cpus(), and I thought num_present_cpus() wouldn't have the
> correct value. nr_cpu_ids seemed close to the value, but then I convinced
> myself NR_CPUS would be okay.
Not specific to this patch: Using NR_CPUS is almost never okay. It's a last
resort if you need a static upper bound. But NR_CPUS can be _much_ larger
than nr_cpu_ids, and hence arrays generally want dimensioning (allocating)
by using the latter.
Jan
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