Re: [PATCH 1/2] viridian: remove implicit limit of 64 VPs per partition

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 08/01/2021 09:19, Jan Beulich wrote:
> On 08.01.2021 01:46, Igor Druzhinin wrote:
>> --- a/tools/libs/light/libxl_x86.c
>> +++ b/tools/libs/light/libxl_x86.c
>> @@ -336,7 +336,7 @@ static int hvm_set_viridian_features(libxl__gc *gc, 
>> uint32_t domid,
>>          LOG(DETAIL, "%s group enabled", 
>> libxl_viridian_enlightenment_to_string(v));
>>  
>>      if (libxl_bitmap_test(&enlightenments, 
>> LIBXL_VIRIDIAN_ENLIGHTENMENT_BASE)) {
>> -        mask |= HVMPV_base_freq;
>> +        mask |= HVMPV_base_freq | HVMPV_no_vp_limit;
> 
> Could you clarify the point of having the new control when at
> the guest config level there's no way to prevent it from
> getting enabled (short of disabling Viridian extensions
> altogether)?

If you migrate in from a host without this code (previous version
of Xen)- you will keep the old behavior for the guest thus preserving
binary compatibility.

Igor