virtio-mem: don't read big block size in Sub Block Mode

We are reading a Big Block Mode value while in Sub Block Mode
when initializing. Fortunately, vm->bbm.bb_size maps to some counter
in the vm->sbm.mb_count array, which is 0 at that point in time.

No harm done; still, this was unintended and is not future-proof.

Fixes: 4ba50cd3355d ("virtio-mem: Big Block Mode (BBM) memory hotplug")
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-2-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 10ec60d..3bf08b5 100644 (file)
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -2420,6 +2420,10 @@ static int virtio_mem_init(struct virtio_mem *vm)
                dev_warn(&vm->vdev->dev,
                         "Some device memory is not addressable/pluggable. This can make some memory unusable.\n");
 
+       /* Prepare the offline threshold - make sure we can add two blocks. */
+       vm->offline_threshold = max_t(uint64_t, 2 * memory_block_size_bytes(),
+                                     VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD);
+
        /*
         * We want subblocks to span at least MAX_ORDER_NR_PAGES and
         * pageblock_nr_pages pages. This:
@@ -2466,14 +2470,11 @@ static int virtio_mem_init(struct virtio_mem *vm)
                       vm->bbm.bb_size - 1;
                vm->bbm.first_bb_id = virtio_mem_phys_to_bb_id(vm, addr);
                vm->bbm.next_bb_id = vm->bbm.first_bb_id;
-       }
 
-       /* Prepare the offline threshold - make sure we can add two blocks. */
-       vm->offline_threshold = max_t(uint64_t, 2 * memory_block_size_bytes(),
-                                     VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD);
-       /* In BBM, we also want at least two big blocks. */
-       vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
-                                     vm->offline_threshold);
+               /* Make sure we can add two big blocks. */
+               vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
+                                             vm->offline_threshold);
+       }
 
        dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
        dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);