Subject: Re: [PATCH 2/4] xen: limit grant v2 interface to the v1 functionality
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org
References: <20170908144849.2958-1-jgross@suse.com>
 <20170908144849.2958-3-jgross@suse.com>
 <f9cc6652-c524-bf4f-73f0-494d16deedf0@oracle.com>
From: Juergen Gross <jgross@suse.com>
Message-ID: <8c87dc06-bbc8-5279-d135-d3351032913d@suse.com>
Date: Tue, 12 Sep 2017 17:50:27 +0200
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On 12/09/17 17:44, Boris Ostrovsky wrote:
> On 09/08/2017 10:48 AM, Juergen Gross wrote:
>> As there is currently no user for sub-page grants or transient grants
>> remove that functionality. This at once makes it possible to switch
>> from grant v2 to grant v1 without restrictions, as there is no loss of
>> functionality other than the limited frame number width related to
>> the switch.
> 
> But isn't that ABI violation? v2 is expected to support this (XSAs
> notwithstanding)

No, I don't think so.

The hypervisor still supports it, but the domU (or dom0) isn't required
to make use of all the features IMHO. Or are you aware of any backend
querying the grant version of a frontend and acting in another way if v2
is detected?


Juergen