Re: [Xen-devel] [PATCH] libxc: fix xc_gntshr_munmap semantic

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-04-30 at 14:21 +0100, Daniel De Graaf wrote:
> On 04/30/2013 06:39 AM, Ian Campbell wrote:
> > On Fri, 2013-04-26 at 17:17 +0100, Daniel De Graaf wrote:
> >> On 04/26/2013 11:26 AM, Ian Campbell wrote:
> >>> On Fri, 2013-04-26 at 16:15 +0100, Daniel De Graaf wrote:
> >>>> On 04/26/2013 10:44 AM, Ian Campbell wrote:
> >>>>> On Fri, 2013-04-26 at 13:40 +0100, Marek Marczykowski wrote:
> >>>>>> "count" parameter should be pages count (as stated in comment in
> >>>>>> xenctrl.h), not bytes count.
> >>>>>> This patch fixes also the only user of this function (in xen sources) -
> >>>>>> libvchan.
> >>>>>
> >>>>> Looks ok to me but Daniel De Graaf wrote all this stuff, Ccing him.
> >>>>
> >>>> This also looks good to me.
> >>>
> >>> May I take that as an Ack (or a Reviewed-by if you prefer)?
> >>
> >> Yes, either one is fine.
> >>
> >> Acked-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> >
> > Is the change from munmap to xc_gntshr_munmap, which wasn't mentioned in
> > the changelog description (tut tut), correct? It seems like these
> > mappings can either be establish with xc_gntshr_share_pages or with "=
> > ((void*)ctrl->ring) + LARGE_RING_OFFSET", with the second one being the
> > case I'm concerned about... Should it not duplicate the switch used at
> > mapping time?
> >
> > Ian.
> >
> 
> The unmap is only done if (ctrl->read.order >= PAGE_SHIFT), which is a
> functional duplicate of the switch statement.

It's a pretty opaque transformation ;-)

But for e.g. order 9, it isn't the same is it? The switch on alloc will
hit the default case while the free won't hit this if statement.

>  However, this does bring
> up a different issue: the munmap() should be replaced with the correct
> one of xc_gntshr_munmap and xc_gnttab_munmap depending on ctrl->is_server,
> in the same way as ctrl->ring is unmapped.

OK, I take it the Ack is rescinded for the time being?

Ian.


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