iommu/amd: Use only natural aligned flushes in a VM

When running on an AMD vIOMMU, it is better to avoid TLB flushes
of unmodified PTEs. vIOMMUs require the hypervisor to synchronize the
virtualized IOMMU's PTEs with the physical ones. This process induce
overheads.

AMD IOMMU allows us to flush any range that is aligned to the power of
2. So when running on top of a vIOMMU, break the range into sub-ranges
that are naturally aligned, and flush each one separately. This apporach
is better when running with a vIOMMU, but on physical IOMMUs, the
penalty of IOTLB misses due to unnecessary flushed entries is likely to
be low.

Repurpose (i.e., keeping the name, changing the logic)
domain_flush_pages() so it is used to choose whether to perform one
flush of the whole range or multiple ones to avoid flushing unnecessary
ranges. Use NpCache, as usual, to infer whether the IOMMU is physical or
virtual.

Cc: Joerg Roedel <joro@8bytes.org>
Cc: Will Deacon <will@kernel.org>
Cc: Jiajun Cao <caojiajun@vmware.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: iommu@lists.linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
Link: https://lore.kernel.org/r/20210723093209.714328-8-namit@vmware.com


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