Re: RFC: Using grant table to give iomem permission

[Keir Fraser <keir@xensource.com>]

On 18/5/07 15:14, "Kieran Mansley" <kmansley@solarflare.com> wrote:

>>> 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.

I'm not sure what you mean.

> 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.

Yes, I misled you here. You want the middle bit of get_page_from_l1e(). It
checks for !mfn_valid()||page_get_owner()==dom_io. Then you'd do an
iomem_access_permitted check passing in a pointer to the granting domain.

You should perhaps pull the core of get_page_from_l1e() into a supporting
function which you can then make available for common/grant_table.c to call
into.

 -- Keir