On Sun, Aug 09, 2026 at 06:20:00PM +0000, Alexander Graf wrote: > Callers that forget to handle a mapping failure may accidentally pass > DMA_MAPPING_ERROR as target map address and we don't error out for it. > The mapped path in vring_map_one_sg() checks the result, but the > premapped path takes the address as given. That makes it more difficult > to identify accidental API misuse.
Nah. We don't spread null checks all over the place and this is the same. > > Run the address through the existing vring_mapping_error(), which asks > the device's virtio_map_ops mapping_error op or dma_mapping_error(), > warn once and return -ENOMEM when it rejects the address. Document > where the premapped helpers expect their addresses to come from, since > an address from any other source is indistinguishable from a valid one. > That way an API misuse shows up at the call that made it. Commit log does not match what doc patches do. > Assisted-by: Kiro:claude-opus-5 checkpatch sparse > Signed-off-by: Alexander Graf <[email protected]> > --- > drivers/virtio/virtio_ring.c | 40 ++++++++++++++++++++++++++++++++++-- > 1 file changed, 38 insertions(+), 2 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index b438dc2ce1b8..9caa4f96204f 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -499,6 +499,19 @@ static int vring_map_one_sg(const struct vring_virtqueue > *vq, struct scatterlist > if (premapped) { > *addr = sg_dma_address(sg); > *len = sg_dma_len(sg); > + > + /* > + * The caller mapped this itself, so the map it used is the > + * only thing that can judge the result. Ask it rather than > + * skipping the check the mapped path performs: a caller that > + * ignored a failed mapping would otherwise publish the > + * reserved error value to the device. > + */ > + if (dev_WARN_ONCE(&vq->vq.vdev->dev, > + vring_mapping_error(vq, *addr), > + "premapped buffer holds no valid mapping\n")) > + return -ENOMEM; > + > return 0; > } > > @@ -2910,6 +2923,14 @@ EXPORT_SYMBOL_GPL(virtqueue_add_outbuf); > * @data: the token identifying the buffer. > * @gfp: how to do memory allocations (if necessary). > * > + * Each entry of @sg must carry an address the caller obtained for this > + * virtqueue: from the DMA API when virtqueue_dma_dev() returns a device, and > + * from virtqueue_map_page_attrs() when it returns NULL, because the device > + * then interprets every address published to it in its own terms. Only an > + * address the map itself rejects is caught here; an address from any other > + * source is indistinguishable from a valid one and reaches the device > + * unchanged. > + * > * Caller must ensure we don't call this with other virtqueue operations > * at the same time (except where noted). > * > @@ -3008,6 +3029,14 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx); > * @ctx: extra context for the token > * @gfp: how to do memory allocations (if necessary). > * > + * Each entry of @sg must carry an address the caller obtained for this > + * virtqueue: from the DMA API when virtqueue_dma_dev() returns a device, and > + * from virtqueue_map_page_attrs() when it returns NULL, because the device > + * then interprets every address published to it in its own terms. Only an > + * address the map itself rejects is caught here; an address from any other > + * source is indistinguishable from a valid one and reaches the device > + * unchanged. I don't see what this comment gets us. And let's not do this half hearted validation. > + * > * Caller must ensure we don't call this with other virtqueue operations > * at the same time (except where noted). > * > @@ -3025,10 +3054,17 @@ int virtqueue_add_inbuf_premapped(struct virtqueue > *vq, > EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_premapped); > > /** > - * virtqueue_dma_dev - get the dma dev > + * virtqueue_dma_dev - get the device to use for DMA API calls > * @_vq: the struct virtqueue we're talking about. > * > - * Returns the dma dev. That can been used for dma api. > + * A NULL return means this virtqueue publishes no DMA addresses: either it > + * needs no mapping at all, or the device supplies its own virtio_map_ops and > + * interprets every address published to it in its own terms. A caller that > + * maps buffers itself must therefore check for NULL before using the DMA API > + * on this virtqueue's behalf, and use virtqueue_map_page_attrs() when it is, > + * which maps through whichever of the two the device uses. Too verbose and repetetive. E.g. of course people who call virtqueue_dma_dev do it to "map bufers itself". > + * > + * Return: the device to use for DMA API calls, or NULL when there is none. > */ > struct device *virtqueue_dma_dev(struct virtqueue *_vq) > {
