memory-device: Support big alignment requirements

Let's warn instead of bailing out - the worst thing that can happen is
that we'll fail hot/coldplug later. The user got warned, and this should
be rare.

This will be necessary for memory devices with rather big (user-defined)
alignment requirements - say a virtio-mem device with a 2G block size -
which will become important, for example, when supporting vfio in the
future.

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
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: <20201008083029.9504-5-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/mem/memory-device.c

@@ -119,9 +119,10 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
 
     /* start of address space indicates the maximum alignment we expect */
     if (!QEMU_IS_ALIGNED(range_lob(&as), align)) {
-        error_setg(errp, "the alignment (0x%" PRIx64 ") is not supported",
-                   align);
-        return 0;
+        warn_report("the alignment (0x%" PRIx64 ") exceeds the expected"
+                    " maximum alignment, memory will get fragmented and not"
+                    " all 'maxmem' might be usable for memory devices.",
+                    align);
     }
 
     memory_device_check_addable(ms, size, &err);
@@ -151,7 +152,7 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
             return 0;
         }
     } else {
-        if (range_init(&new, range_lob(&as), size)) {
+        if (range_init(&new, QEMU_ALIGN_UP(range_lob(&as), align), size)) {
             error_setg(errp, "can't add memory device, device too big");
             return 0;
         }