[Hardy(Xen)]: SRU request for LP#247148

[Stefan Bader]

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/247148

SRU justification:

Impact: Using SWIOMMU unnecessarily causes "out of space" errors and 
subsequently causes corruptions in software RAID (and probably also caused the 
problems mentioned in 
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/238118/comments/9).

Fix: (taken from the Xen changelog) This patch adds a new check, 
check_pages_physically_contiguous(), to the test for pages stradding page 
boundaries both in swiotlb_map_sg() and dma_map_sg(), to capture these ranges 
and map them directly via virt_to_bus() mapping rather than through the swiotlb.

Testcase: IO errors when doing increased workload on SCSI drives (see bug report)

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