iommupt: Flush the CPU cache after any writes to the page table

iommupt: Flush the CPU cache after any writes to the page table

Flush the CPU cache for the page table memory after each set of writes to
the page table. The iommu should have visibility to the updated entries as
soon as the map/unmap/etc operations return, like normal coherent hardware
does.

The caches also have to be flushed before any gather can be submitted to
the driver.

Implement the same solution to the race as io-pgtable-arm by using a
software PTE bit to track if a table entry has been flushed or not. If
another thread is still flushing then another concurrent map operation
could return without IOMMU visibility to a required table entry. The SW
bit will tell the second thread to also flush the cache.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>