blkio: Respect memory-alignment for bounce buffer allocations

blkio_alloc_mem_region() requires that the requested buffer size is a
multiple of the memory-alignment property. If it isn't, the allocation
fails with a return value of -EINVAL.

Fix the call in blkio_resize_bounce_pool() to make sure the requested
size is properly aligned.

I observed this problem with vhost-vdpa, which requires page aligned
memory. As the virtio-blk device behind it still had 512 byte blocks, we
got bs->bl.request_alignment = 512, but actually any request that needed
a bounce buffer and was not aligned to 4k would fail without this fix.

Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20240131173140.42398-1-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/block/blkio.c b/block/blkio.c
index bc2f21784c..882e1c297b 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -89,6 +89,9 @@ static int blkio_resize_bounce_pool(BDRVBlkioState *s, int64_t bytes)
     /* Pad size to reduce frequency of resize calls */
     bytes += 128 * 1024;
 
+    /* Align the pool size to avoid blkio_alloc_mem_region() failure */
+    bytes = QEMU_ALIGN_UP(bytes, s->mem_region_alignment);
+
     WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         int ret;