Re: [Xen-devel] [PATCH v8 0/8] xen/arm: introduce GNTTABOP_cache_flush

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 20 Oct 2014, Jan Beulich wrote:
> >>> On 20.10.14 at 11:47, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > Hi all,
> > this patch series introduces a new hypercall to perform cache
> > maintenance operations on behalf of the guest. It is useful for dom0 to
> > be able to cache flush pages involved in a dma operation with
> > non-coherent devices.
> > 
> > It also removes XENFEAT_grant_map_identity as the feature is no longer
> > necessary: it was used to achieve the same goal but the guest can now
> > use the hypercall instead. Keeping the flag would also have a
> > significant performance impact as a new p2m mapping gets created and
> > then destroyed for every grant that is mapped and unmapped in dom0.
> > 
> > 
> > Changes in v8:
> > - remove unused #include;
> > - set max_nr_grant_frames as __initdata;
> > - set max_grant_frames and max_maptrack_frames as __read_mostly;
> > - respent coding style for comments;
> > - remove MAX_MAPTRACK_TO_GRANTS_RATIO;
> > - avoid security issues, use two separate opaque variables to store the
> > input argument and the output argument;
> 
> Security issues?

The user could have passed in an opaque value for a gnttabop that
doesn't use it, causing Xen to keep looping over the continuation.
I fixed it by using two different variable to save the opaque input and
output.

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