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[Xen-devel] Re: RFC: Using grant table to give iomem permission

On Fri, 2007-05-18 at 15:05 +0100, Keir Fraser wrote:
> On 18/5/07 15:01, "Kieran Mansley" <kmansley@xxxxxxxxxxxxxx> wrote:
> > When finished, the mapping domain can similarly unmap the grant, which
> > removes its ability to ioremap() the page:
> > struct gnttab_unmap_grant_ref op;
> > gnttab_set_unmap_op(&op, 0, GNTMAP_iomem_map, handle);
> > if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
> > BUG();
> > 
> > Some questions from me:
> >  - does this approach seem sane?
> There's no reason you shouldn't be able to use GNTMAP_host_map as usual, and
> do refcounting in the active grant entry, also as usual.

OK.  My reluctance to do that was simply that I wasn't sure if the
operations that take place when doing a GNTMAP_host_map would conflict
with those when doing an iomem_map.  If you think they shouldn't, I'll
give it a go.

That raises one of my other questions which is how to test for it being
a valid RAM page, as in the absence of it GNTMAP_iomem_map that's pretty
much the only indicator that it's iomem we're dealing with.  As I said,
mfn_valid() doesn't seem to be sufficient.


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