virtio-blk: correctly dirty guest memory
After qemu_iovec_destroy, the QEMUIOVector's size is zeroed and
the zero size ultimately is used to compute virtqueue_push's len
argument. Therefore, reads from virtio-blk devices did not
migrate their results correctly. (Writes were okay).
Save the size in virtio_blk_handle_request, and use it when the request
is completed.
Based on a patch by Wen Congyang.
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Message-id: 1427997044-392-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 000c38d..9546fd2 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -33,6 +33,7 @@
VirtIOBlockReq *req = g_slice_new(VirtIOBlockReq);
req->dev = s;
req->qiov.size = 0;
+ req->in_len = 0;
req->next = NULL;
req->mr_next = NULL;
return req;
@@ -54,7 +55,7 @@
trace_virtio_blk_req_complete(req, status);
stb_p(&req->in->status, status);
- virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in));
+ virtqueue_push(s->vq, &req->elem, req->in_len);
virtio_notify(vdev, s->vq);
}
@@ -102,6 +103,14 @@
if (ret) {
int p = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type);
bool is_read = !(p & VIRTIO_BLK_T_OUT);
+ /* Note that memory may be dirtied on read failure. If the
+ * virtio request is not completed here, as is the case for
+ * BLOCK_ERROR_ACTION_STOP, the memory may not be copied
+ * correctly during live migration. While this is ugly,
+ * it is acceptable because the device is free to write to
+ * the memory until the request is completed (which will
+ * happen on the other side of the migration).
+ */
if (virtio_blk_handle_rw_error(req, -ret, is_read)) {
continue;
}
@@ -496,6 +505,8 @@
exit(1);
}
+ /* We always touch the last byte, so just see how big in_iov is. */
+ req->in_len = iov_size(in_iov, in_num);
req->in = (void *)in_iov[in_num - 1].iov_base
+ in_iov[in_num - 1].iov_len
- sizeof(struct virtio_blk_inhdr);
