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Re: [Xen-devel] [PATCH linux-2.6.18] xen: mark pvscsi frontend request consumed only after last read

On 02/02/2015 08:52 AM, Jan Beulich wrote:
On 30.01.15 at 14:51, <"jgross@xxxxxxxx".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

Hence - also considering with my earlier reply - I don't view the change
as necessary.



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