Re: [PATCH v2] gnttab: defer allocation of status frame tracking array

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.01.2021 16:04, Andrew Cooper wrote:
> On 23/12/2020 15:13, Jan Beulich wrote:
>> This array can be large when many grant frames are permitted; avoid
>> allocating it when it's not going to be used anyway, by doing this only
>> in gnttab_populate_status_frames().
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> v2: Defer allocation to when a domain actually switches to the v2 grant
>>     API.
> 
> I see this as a backwards step.  It turns a build-time -ENOMEM into a
> runtime -ENOMEM, and if you recall from one of the XSAs, the Windows PV
> drivers will BUG() if set_version fails.  (Yes - this is dumb behaviour,
> but it is in the field now.)

Well, if this was the only source of -ENOMEM (i.e. none was there
previously), I'd surely understand the concern. But there have been
memory allocations before on this path. In any event, this will
need settling between you and Julien, as it was him to request the
change.

Jan