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

From: Jan Beulich <jbeulich@suse.com>
To: Ian Jackson <iwj@xenproject.org>
Cc: xen-devel@lists.xenproject.org, Wei Liu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Anthony PERARD <anthony.perard@citrix.com>,
	Juergen Gross <jgross@suse.com>,
	Christian Lindig <christian.lindig@citrix.com>,
	David Scott <dave@recoil.org>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH for-4.16 v6] gnttab: allow setting max version per-domain
Date: Thu, 4 Nov 2021 13:25:31 +0100	[thread overview]
Message-ID: <8ae2c1ac-b220-a5ab-920b-244590ae3ef0@suse.com> (raw)
In-Reply-To: <24963.52610.316896.770905@mariner.uk.xensource.com>

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@citrix.com/
> 
> 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