virtio-mem: Make sure "addr" is always multiples of the block size

virtio-mem: Make sure "addr" is always multiples of the block size

The spec states:
  "The device MUST set addr, region_size, usable_region_size, plugged_size,
   requested_size to multiples of block_size."

In some cases, we currently don't guarantee that for "addr": For example,
when starting a VM with 4 GiB boot memory and a virtio-mem device with a
block size of 2 GiB, "memaddr"/"addr" will be auto-assigned to
0x140000000 (5 GiB).

We'll try to improve auto-assignment for memory devices next, to avoid
bailing out in case memory device code selects a bad address.

Note: The Linux driver doesn't support such big block sizes yet.

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Fixes: 910b25766b33 ("virtio-mem: Paravirtualized memory hot(un)plug")
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20201008083029.9504-2-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>