On Wed, May 17, 2023 at 10:23 AM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> virtqueue_add_split() only supports virtual addresses, dma is completed
> in virtqueue_add_split().
>
> In some scenarios (such as the AF_XDP scenario), the memory is allocated
> and DMA is completed in advance, so it is necessary for us to support
> passing the DMA address to virtqueue_add_split().
>
> Record this information in desc_state, we can skip unmap based on this
> when executing dma unmap.
I would also suggest documenting why a per descriptor metadata is
needed instead of a per virtqueue one.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
> drivers/virtio/virtio_ring.c | 38 +++++++++++++++++++++++++++---------
> 1 file changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index e2fc50c05bec..bd5e84afab37 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -70,6 +70,7 @@
> struct vring_desc_state_split {
> void *data; /* Data for callback. */
> struct vring_desc *indir_desc; /* Indirect descriptor, if any. */
> + bool premapped; /* DMA mapping is done by driver. */
Going back to the original discussion around where this should be
placed. I wonder if we can find a common place to store this since it
has nothing related to virtqueue layout. Maybe desc_extra? And it
would be even better if we can avoid stressing the cache like above.
> };
>
> struct vring_desc_state_packed {
> @@ -356,8 +357,14 @@ static struct device *vring_dma_dev(const struct vring_virtqueue *vq)
>
> /* Map one sg entry. */
> static int vring_map_one_sg(const struct vring_virtqueue *vq, struct scatterlist *sg,
> - enum dma_data_direction direction, static dma_addr_t *addr)
> + enum dma_data_direction direction,
> + bool premapped, dma_addr_t *addr)
having things like:
int func(bool do)
{
if (!do)
return;
}
is a hint that the check needs to be done by the caller?
And this change should work for both packed and split. I think we need
to squash the packed changes here.
Looking at how packed virtqueue uses this in this patch, I don't think
this patch can even be built. I will wait for a new version and
continue the review from there.
Thanks
> {
> + if (premapped) {
> + *addr = sg_dma_address(sg);
> + return 0;
> + }
> +
> if (!vq->use_dma_api) {
> /*
> * If DMA is not used, KMSAN doesn't know that the scatterlist
> @@ -445,7 +452,7 @@ static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
> }
>
> static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> - unsigned int i)
> + unsigned int i, bool premapped)
> {
> struct vring_desc_extra *extra = vq->split.desc_extra;
> u16 flags;
> @@ -462,6 +469,9 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> (flags & VRING_DESC_F_WRITE) ?
> DMA_FROM_DEVICE : DMA_TO_DEVICE);
> } else {
> + if (premapped)
> + goto out;
> +
> dma_unmap_page(vring_dma_dev(vq),
> extra[i].addr,
> extra[i].len,
> @@ -532,6 +542,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> unsigned int in_sgs,
> void *data,
> void *ctx,
> + bool premapped,
> gfp_t gfp)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> @@ -595,7 +606,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> dma_addr_t addr;
>
> - if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, &addr))
> + if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, premapped, &addr))
> goto unmap_release;
>
> prev = i;
> @@ -611,7 +622,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> dma_addr_t addr;
>
> - if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, &addr))
> + if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, premapped, &addr))
> goto unmap_release;
>
> prev = i;
> @@ -657,6 +668,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>
> /* Store token and indirect buffer state. */
> vq->split.desc_state[head].data = data;
> + vq->split.desc_state[head].premapped = premapped;
> if (indirect)
> vq->split.desc_state[head].indir_desc = desc;
> else
> @@ -686,6 +698,14 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> return 0;
>
> unmap_release:
> + if (premapped) {
> + if (indirect)
> + kfree(desc);
> +
> + END_USE(vq);
> + return -ENOMEM;
> + }
> +
> err_idx = i;
>
> if (indirect)
> @@ -700,7 +720,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> vring_unmap_one_split_indirect(vq, &desc[i]);
> i = virtio16_to_cpu(_vq->vdev, desc[i].next);
> } else
> - i = vring_unmap_one_split(vq, i);
> + i = vring_unmap_one_split(vq, i, false);
> }
>
> if (indirect)
> @@ -757,12 +777,12 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> i = head;
>
> while (vq->split.vring.desc[i].flags & nextflag) {
> - vring_unmap_one_split(vq, i);
> + vring_unmap_one_split(vq, i, state->premapped);
> i = vq->split.desc_extra[i].next;
> vq->vq.num_free++;
> }
>
> - vring_unmap_one_split(vq, i);
> + vring_unmap_one_split(vq, i, state->premapped);
> vq->split.desc_extra[i].next = vq->free_head;
> vq->free_head = head;
>
> @@ -783,7 +803,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> VRING_DESC_F_INDIRECT));
> BUG_ON(len == 0 || len % sizeof(struct vring_desc));
>
> - if (vq->use_dma_api) {
> + if (vq->use_dma_api && !state->premapped) {
> for (j = 0; j < len / sizeof(struct vring_desc); j++)
> vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> }
> @@ -2143,7 +2163,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
> return vq->packed_ring ? virtqueue_add_packed(_vq, sgs, total_sg,
> out_sgs, in_sgs, data, ctx, gfp) :
> virtqueue_add_split(_vq, sgs, total_sg,
> - out_sgs, in_sgs, data, ctx, gfp);
> + out_sgs, in_sgs, data, ctx, premapped, gfp);
> }
>
> /**
> --
> 2.32.0.3.g01195cf9f
>
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