iommu/amd: Fix domain flush size when syncing iotlb

When running on an AMD vIOMMU, we observed multiple invalidations (of
decreasing power of 2 aligned sizes) when unmapping a single page.

Domain flush takes gather bounds (end-start) as size param. However,
gather->end is defined as the last inclusive address (start + size - 1).
This leads to an off by 1 error.

With this patch, verified that 1 invalidation occurs when unmapping a
single page.

Fixes: a270be1b ("iommu/amd: Use only natural aligned flushes in a VM")
Cc: stable@vger.kernel.org # >= 5.15
Signed-off-by: Jon Pan-Doh <pandoh@google.com>
Tested-by: Sudheer Dantuluri <dantuluris@google.com>
Suggested-by: Gary Zibrat <gzibrat@google.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Acked-by: Nadav Amit <namit@vmware.com>
Link: https://lore.kernel.org/r/20230426203256.237116-1-pandoh@google.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>