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.
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. 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. + * * 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. + * + * Return: the device to use for DMA API calls, or NULL when there is none. */ struct device *virtqueue_dma_dev(struct virtqueue *_vq) {
