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[Xen-devel] [PATCHv4 00/14] xen: fix many long-standing grant mapping bugs

This series fixes a number of long-standing bugs in the handling of
grant maps.  Refer to the following for all the details.


In summary, the important uses that this enables are:

1. Block backends can use networked storage safely.

2. Block backends can use network storage provided by other guests on
   the same host.

3. User space block backends can use direct I/O or asynchronous I/O.

The first two patches are the core MM changes necessary.  These have
already been acked.

Patches #3 and #4 remove existing (broken) mechanisms.  This does
temporarily break some previously working use cases, but it does make
the subsequent additions much easier to review.

As a happy side effect, performance is also likely to be improved in
some areas (but I've not got any measurements yet).  User space
backends using grant mapping should see some good improvements from
reduced overheads and better unmap batching.  VIF to VIF network
traffic may also see a small improvement.

Finally, thanks to Jenny who did much of the implementation.

Changes in v4:
- Removed xen_blkbk_unmap_done().
- Fixed bug in blkback when using mixed persistent and non-persistent

Changes in v3:
- find_page renamed to find_special_page.
- Added documentation for mm changes.
- Fixed mangled forward port of blkback's safe unmap patch.
- Export gnttab_alloc_pages() and gnttab_free_pages().
- Fix 32-bit build.

Changes in v2:
- Add find_page() VMA op instead of pages field (so struct
  vm_area_struct doesn't increase in size.
- Make foreign page tracking arch-independant and improve the API.
- Alloc extra memory (for 32-bit archs) for the (domain, gref) when
  allocating the page (instead of during the map).
- Convert gntdev's lock to a mutex.


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