Re: [Xen-devel] GNTTABOP_unmap_grant_ref

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25 Jan 2006, at 01:33, King, Steven R wrote:

> To verify that I wasn't making some new mistake, inspection of
> linux/mm/mmap.c shows that Linux calls vma->close() *after* the page
> table manipulation.  In do_munmap(), the sequence is:
>
> detach_vmas_to_be_unmapped()
> unmap_region()       <--- page table manipulation buried in here
> remove_vma_list()    <--- vma->close() buried in here
As others have suggested, you need a special type of vma that knows how 
to map/unmap/destruct ranges of granted mappings. A good way to do this 
would be to have gnttab.c export a device file that has an mmap() 
function. You can then add vma hook functions that know that any 
mapping created in that vma range must be destructed via gnt_unmap 
operations.
> Is this turning into a Xen problem?  Why does Xen forbid implicit
> unmapping of shared pages?
It's hard for Xen to distinguish between mappings created via grants 
vs. mappings created because domain X is privileged to be able to map 
any page of domain Y.
So far we've only really had grant-mapping code in the kernel. Doing it 
in user space just needs some work on the clean-up path. We expect 
guests to track and clean up their own mess. :-)
 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel