On Wed, 2015-02-04 at 02:41 -0800, Nicholas A. Bellinger wrote:
> On Wed, 2015-02-04 at 10:42 +0100, Michael S. Tsirkin wrote:
> > On Wed, Feb 04, 2015 at 01:40:25AM -0800, Nicholas A. Bellinger wrote:
> > > > > + /*
> > > > > + * Any associated T10_PI bytes for the outgoing / incoming
> > > > > + * payloads are included in calculation of exp_data_len here.
> > > > > + */
> > > > > + if (out_size > req_size) {
> > > > > + data_direction = DMA_TO_DEVICE;
> > > > > + exp_data_len = out_size - req_size;
> > > > > + } else if (in_size > rsp_size) {
> > > > > + data_direction = DMA_FROM_DEVICE;
> > > > > + exp_data_len = in_size - rsp_size;
> > > > > + } else {
> > > > > + data_direction = DMA_NONE;
> > > > > + exp_data_len = 0;
> > > > > + }
> > > >
> > > > We must validate this doesn't cause exp_data_len to be negative.
> > > >
> > >
> > > AFAICT, exp_data_len is always >= 0 here.
> >
> > What guarantees out_size > req_size and in_size > rsp_size,
> > respectively?
> >
>
> Mmm, point taken.
>
> So moving this part after copy_from_iter() ensures that at least
> req_size bytes exists of out_size. Making this change now.
>
> For in_size > rsp_size there is no guarantee, and falls back to
> data_direction = DMA_NONE + exp_data_len = 0;
>
> Is this what you had in mind..?
>
Something akin to:
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index f72fc56..daf10b7 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1047,30 +1047,12 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
target = &v_req.lun[1];
}
/*
- * Determine data_direction by calculating the total outgoing
- * iovec sizes / incoming iovec sizes vs. virtio-scsi request /
- * response headers respectively.
- *
* FIXME: Not correct for BIDI operation
*/
out_size = iov_length(vq->iov, out);
in_size = iov_length(&vq->iov[out], in);
/*
- * Any associated T10_PI bytes for the outgoing / incoming
- * payloads are included in calculation of exp_data_len here.
- */
- if (out_size > req_size) {
- data_direction = DMA_TO_DEVICE;
- exp_data_len = out_size - req_size;
- } else if (in_size > rsp_size) {
- data_direction = DMA_FROM_DEVICE;
- exp_data_len = in_size - rsp_size;
- } else {
- data_direction = DMA_NONE;
- exp_data_len = 0;
- }
- /*
* Copy over the virtio-scsi request header, which for a
* ANY_LAYOUT enabled guest may span multiple iovecs, or a
* single iovec may contain both the header + outgoing
@@ -1102,8 +1084,9 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
continue;
}
/*
- * Determine start of T10_PI or data payload iovec based upon
- * data_direction.
+ * Determine data_direction by calculating the total outgoing
+ * iovec sizes + incoming iovec sizes vs. virtio-scsi request +
+ * response headers respectively.
*
* For DMA_TO_DEVICE this is out_iter, which is already pointing
* to the right place.
@@ -1111,16 +1094,27 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
* For DMA_FROM_DEVICE, the iovec will be just past the end
* of the virtio-scsi response header in either the same
* or immediately following iovec.
+ *
+ * Any associated T10_PI bytes for the outgoing / incoming
+ * payloads are included in calculation of exp_data_len here.
*/
prot_bytes = 0;
- if (data_direction == DMA_TO_DEVICE) {
+ if (out_size > req_size) {
+ data_direction = DMA_TO_DEVICE;
+ exp_data_len = out_size - req_size;
data_iter = out_iter;
- } else if (data_direction == DMA_FROM_DEVICE) {
+ } else if (in_size > rsp_size) {
+ data_direction = DMA_FROM_DEVICE;
+ exp_data_len = in_size - rsp_size;
+
iov_iter_init(&in_iter, READ, &vq->iov[out], in,
rsp_size + exp_data_len);
iov_iter_advance(&in_iter, rsp_size);
data_iter = in_iter;
+ } else {
+ data_direction = DMA_NONE;
+ exp_data_len = 0;
}
/*
* If T10_PI header + payload is present, setup prot_iter values
--
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