Re: [PATCH for-4.16 v6] gnttab: allow setting max version per-domain

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.11.2021 13:09, Ian Jackson wrote:
> Roger Pau Monne writes ("[PATCH for-4.16 v6] gnttab: allow setting max 
> version per-domain"):
>> Introduce a new domain create field so that toolstack can specify the
>> maximum grant table version usable by the domain. This is plumbed into
>> xl and settable by the user as max_grant_version.
>>
>> Previously this was only settable on a per host basis using the
>> gnttab command line option.
>>
>> Note the version is specified using 4 bits, which leaves room to
>> specify up to grant table version 15. Given that we only have 2 grant
>> table versions right now, and a new version is unlikely in the near
>> future using 4 bits seems more than enough.
>>
>> xenstored stubdomains are limited to grant table v1 because the
>> current MiniOS code used to build them only has support for grants v1.
>> There are existing limits set for xenstored stubdomains at creation
>> time that already match the defaults in MiniOS.
> ...
>> This needs to be applied on top of Andrew's:
>>
>> xen: Report grant table v1/v2 capabilities to the toolstack
>> https://lore.kernel.org/xen-devel/20211029173813.23002-1-andrew.cooper3@xxxxxxxxxx/
> 
> Thanks.
> 
> We have discussed this wrt 4.16.  I am minded to grant a release ack
> for this.  If anyone has a contrary opinion please speak now.
> 
> (I think committing both of these would be subject to maintainer acks
> for "Report grant table v1/v2 capabilities", which I didn't see but
> perhaps I am missing.)

Afaic that patch looks okay (albeit not really a scalable way to express
things, if we were to consider further versions to appear), but it wasn't
clear to me whether Roger's reply was meant as an objection, a direction
towards doing things differently, or merely a benign comment. Hence it
didn't feel appropriate to give an A-b just yet.

Jan