[PATCH v1 5/5] virito-mem: Implement get_min_alignment()

[David Hildenbrand <david@redhat.com>]

This allows auto-assignment of a properly aligned address in guest
physical address space. For example, when specifying a 2GB block size
for a virtio-mem device with 10GB with a memory setup "-m 4G, 20G",
we'll no longer fail when realizing.

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>
---
 hw/virtio/virtio-mem-pci.c | 14 ++++++++++++++
 hw/virtio/virtio-mem.c     |  8 ++++++++
 2 files changed, 22 insertions(+)

diff --git a/hw/virtio/virtio-mem-pci.c b/hw/virtio/virtio-mem-pci.c
index 590cec041b..2bfa2474fb 100644
--- a/hw/virtio/virtio-mem-pci.c
+++ b/hw/virtio/virtio-mem-pci.c
@@ -75,6 +75,19 @@ static void virtio_mem_pci_fill_device_info(const MemoryDeviceState *md,
     info->type = MEMORY_DEVICE_INFO_KIND_VIRTIO_MEM;
 }
 
+static uint64_t virtio_mem_pci_get_min_alignment(const MemoryDeviceState *md)
+{
+    /*
+     * If no block size was configured, returns the default block size.
+     * Before the device was realized, this might be smaller than the
+     * final block size (because it ignores the page size of the memory region).
+     * However, the alignment of the memory region properly considers the
+     * page size of the memory region.
+     */
+    return object_property_get_uint(OBJECT(md), VIRTIO_MEM_BLOCK_SIZE_PROP,
+                                    &error_abort);
+}
+
 static void virtio_mem_pci_size_change_notify(Notifier *notifier, void *data)
 {
     VirtIOMEMPCI *pci_mem = container_of(notifier, VirtIOMEMPCI,
@@ -109,6 +122,7 @@ static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
     mdc->get_plugged_size = virtio_mem_pci_get_plugged_size;
     mdc->get_memory_region = virtio_mem_pci_get_memory_region;
     mdc->fill_device_info = virtio_mem_pci_fill_device_info;
+    mdc->get_min_alignment = virtio_mem_pci_get_min_alignment;
 }
 
 static void virtio_mem_pci_instance_init(Object *obj)
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 716eddd792..d8222153cf 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -805,6 +805,14 @@ static void virtio_mem_get_block_size(Object *obj, Visitor *v, const char *name,
     const VirtIOMEM *vmem = VIRTIO_MEM(obj);
     uint64_t value = vmem->block_size;
 
+    /*
+     * If not configured by the user (and we're not realized yet), use the
+     * default block size.
+     */
+    if (!value) {
+        value = virtio_mem_default_block_size();
+    }
+
     visit_type_size(v, name, &value, errp);
 }
 
-- 
2.26.2