iommu/vt-d: Add iotlb_sync_map callback

iommu/vt-d: Add iotlb_sync_map callback

Some Intel VT-d hardware implementations don't support memory coherency
for page table walk (presented by the Page-Walk-coherency bit in the
ecap register), so that software must flush the corresponding CPU cache
lines explicitly after each page table entry update.

The iommu_map_sg() code iterates through the given scatter-gather list
and invokes iommu_map() for each element in the scatter-gather list,
which calls into the vendor IOMMU driver through iommu_ops callback. As
the result, a single sg mapping may lead to multiple cache line flushes,
which leads to the degradation of I/O performance after the commit
<c588072bba6b5> ("iommu/vt-d: Convert intel iommu driver to the iommu
ops").

Fix this by adding iotlb_sync_map callback and centralizing the clflush
operations after all sg mappings.

Fixes: c588072bba6b5 ("iommu/vt-d: Convert intel iommu driver to the iommu ops")
Reported-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/linux-iommu/D81314ED-5673-44A6-B597-090E3CB83EB0@oracle.com/
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Robin Murphy <robin.murphy@arm.com>
[ cel: removed @first_pte, which is no longer used ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/linux-iommu/161177763962.1311.15577661784296014186.stgit@manet.1015granger.net
Link: https://lore.kernel.org/r/20210204014401.2846425-5-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>