From mboxrd@z Thu Jan  1 00:00:00 1970
From: Juergen Gross <jgross@suse.com>
Subject: Re: [PATCH linux-2.6.18] xen: mark pvscsi frontend
 request consumed only after last read
Date: Mon, 02 Feb 2015 11:17:43 +0100
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To: Jan Beulich <JBeulich@suse.com>
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On 02/02/2015 08:52 AM, Jan Beulich wrote:
>>>> On 30.01.15 at 14:51, <"jgross@suse.com".non-mime.internet> wrote:
>> A request in the ring buffer mustn't be read after it has been marked
>> as consumed. Otherwise it might already have been reused by the
>> frontend without violating the ring protocol.
>
> This is irrelevant, as the ->req_cons is a backend private field (if it
> was a shared one, a barrier would have been needed between
> copying and updating that field).

Hmm, you are right. Interesting, I've always thought req_cons would be
used by the frontend, too.

Thanks for updating my protocol know-how. :-)

>
>> To avoid inconsistencies in the backend only work on a private copy
>> of the request. This will ensure a malicious guest not being able to
>> bypass consistency checks of the backend by modifying an active
>> request.
>
> Hence - also considering with my earlier reply - I don't view the change
> as necessary.

Agreed.


Juergen