Re: [PATCH v1 2/2] xen/domain: introduce generic weak function for domain struct allocation

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.06.2025 20:53, Andrew Cooper wrote:
> On 13/06/2025 4:56 pm, Oleksii Kurochko wrote:
>> diff --git a/xen/common/domain.c b/xen/common/domain.c
>> index e566a18747..c134868e95 100644
>> --- a/xen/common/domain.c
>> +++ b/xen/common/domain.c
>> @@ -785,6 +785,20 @@ static int sanitise_domain_config(struct 
>> xen_domctl_createdomain *config)
>>      return arch_sanitise_domain_config(config);
>>  }
>>  
>> +struct domain *__weak alloc_domain_struct(void)
>> +{
>> +    struct domain *d = alloc_xenheap_pages(0, 0);
> 
> I know you're just moving what ARM has, but this is spelt
> alloc_xenheap_page();
> 
>> +
>> +    BUILD_BUG_ON(sizeof(*d) > PAGE_SIZE);
>> +
>> +    if ( !d )
>> +        return NULL;
>> +
>> +    clear_page(d);
>> +
>> +    return d;
>> +}
>> +
> 
> This looks fine, but you must do the same with free_domain_struct() at
> the same time to keep the pair symmetric.  That in turn gets you an even
> bigger negative diffstat, and x86 doesn't even need to override the
> common version.
> 
> vCPU really wants doing at the same time, although you're going to run
> into problems on ARM there with the BUILD_BUG_ON().
> 
> However, I suspect we want to be building with -ffunction-sections
> generally active, or IIRC we'll still have the weak copy present in the
> final image.

Instead of introducing a weak function in common code, why don't we move
the function there altogether, adding merely an arch hook to control the
flags to be passed into alloc_xenheap_pages()?

Jan