Let's try to detect the actual THP size and use it as default block size
(unless the page size of the backend indicates that THP don't apply).
Always allow to set a block size of 1 MiB, but warn if the configured block
size is smaller than the default. Handle large block sizes better, avoiding
a virtio-spec violation and optimizing address auto-detection.

For existing setups (x86-64), the default block size won't change (was, and
will be 2 MiB on anonymous memory). For existing x86-64 setups, the address
auto-detection won't change in relevant setups (esp., anonymous memory
and hugetlbfs with 2 MiB pages and no manual configuration of the block
size). I don't see the need for compatibility handling (especially, as
virtio-mem is still not considered production-ready).

Most of this is a preparation for future architectures, using hugetlbfs
to full extend, and using manually configured, larger block sizes
(relevant for vfio in the future).

v1 -> v2:
- Tweak some patch descriptions
- "virtio-mem: Probe THP size to determine default block size"
-- Beautify THP detection a bit.
-- Assume THP might only get used if the memory backend page size corresponds
   to the real hostpage size.
-- Use virtio_mem_default_block_size(RAMBlock *rb) to handle selection
   of the default block size for a RAMBlock.
-- Implement virtio_mem_get_block_size() as preparation for patch #5
- "memory-device: Add get_min_alignment() callback"
-- Simplify documentation.
- "virito-mem: Implement get_min_alignment()"
-- Simplify due to changes in patch #1.

David Hildenbrand (5):
  virtio-mem: Probe THP size to determine default block size
  virtio-mem: Check that "memaddr" is multiples of the block size
  memory-device: Support big alignment requirements
  memory-device: Add get_min_alignment() callback
  virito-mem: Implement get_min_alignment()

 hw/mem/memory-device.c         |  20 ++++--
 hw/virtio/virtio-mem-pci.c     |   7 +++
 hw/virtio/virtio-mem.c         | 110 +++++++++++++++++++++++++++++++--
 include/hw/mem/memory-device.h |  10 +++
 4 files changed, 137 insertions(+), 10 deletions(-)

-- 
2.26.2