On Tue, 14 Mar 2023 15:05:58 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> On Wed, Mar 8, 2023 at 2:44 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> >
> > DMA-related logic is separated from the virtqueue_add_split() to
> > one new function. DMA address will be saved as sg->dma_address, then
> > virtqueue_add_split() will use it directly. Unmap operation will be
> > simpler.
> >
> > The purpose of this is to facilitate subsequent support to receive
> > dma address mapped by drivers.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > ---
> > drivers/virtio/virtio_ring.c | 110 ++++++++++++++++++++++++++---------
> > 1 file changed, 82 insertions(+), 28 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 41144b5246a8..8ace2f503953 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -520,6 +520,77 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
> > return next;
> > }
> >
> > +static void virtqueue_unmap_sgs(struct vring_virtqueue *vq,
> > + struct scatterlist *sgs[],
> > + unsigned int total_sg,
> > + unsigned int out_sgs,
> > + unsigned int in_sgs)
> > +{
> > + struct scatterlist *sg;
> > + unsigned int n;
> > +
> > + if (!vq->use_dma_api)
> > + return;
> > +
> > + for (n = 0; n < out_sgs; n++) {
> > + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > + if (!sg->dma_address)
> > + return;
> > +
> > + dma_unmap_page(vring_dma_dev(vq), sg->dma_address,
> > + sg->length, DMA_TO_DEVICE);
> > + }
> > + }
> > +
> > + for (; n < (out_sgs + in_sgs); n++) {
> > + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > + if (!sg->dma_address)
> > + return;
> > +
> > + dma_unmap_page(vring_dma_dev(vq), sg->dma_address,
> > + sg->length, DMA_FROM_DEVICE);
> > + }
> > + }
> > +}
> > +
> > +static int virtqueue_map_sgs(struct vring_virtqueue *vq,
> > + struct scatterlist *sgs[],
> > + unsigned int total_sg,
> > + unsigned int out_sgs,
> > + unsigned int in_sgs)
> > +{
> > + struct scatterlist *sg;
> > + unsigned int n;
> > +
>
> So we have a use_dma_api check in the unmap path but not here. More below.
>
> > + for (n = 0; n < out_sgs; n++) {
> > + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > + dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
> > +
> > + if (vring_mapping_error(vq, addr))
> > + goto err;
> > +
> > + sg->dma_address = addr;
>
> When KMSAN is not enabled (should be the case for production
> environments), the only work that is done here is to assign the
> dma_address. And there will be another loop after the mapping to add
> descriptors, this seems to slow down the performance. Any benchmark
> for this patch? Or can we:
>
> 1) return early when use_dma_api is false
> 2) have a helper like
>
> vring_sg_address() {
> if (!sg->dma_address)
> return sg_phys(sg);
> return sg->dma_address;
> }
LGTM
Thanks.
>
> Thanks
>
> > + }
> > + }
> > +
> > + for (; n < (out_sgs + in_sgs); n++) {
> > + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > + dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
> > +
> > + if (vring_mapping_error(vq, addr))
> > + goto err;
> > +
> > + sg->dma_address = addr;
> > + }
> > + }
> > +
> > + return 0;
> > +
> > +err:
> > + virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
> > + return -ENOMEM;
> > +}
> > +
> > static inline int virtqueue_add_split(struct virtqueue *_vq,
> > struct scatterlist *sgs[],
> > unsigned int total_sg,
> > @@ -532,9 +603,9 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > struct vring_virtqueue *vq = to_vvq(_vq);
> > struct scatterlist *sg;
> > struct vring_desc *desc;
> > - unsigned int i, n, avail, descs_used, prev, err_idx;
> > - int head;
> > + unsigned int i, n, avail, descs_used, prev;
> > bool indirect;
> > + int head;
> >
> > START_USE(vq);
> >
> > @@ -586,32 +657,30 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > return -ENOSPC;
> > }
> >
> > + if (virtqueue_map_sgs(vq, sgs, total_sg, out_sgs, in_sgs))
> > + return -ENOMEM;
> > +
> > for (n = 0; n < out_sgs; n++) {
> > for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > - dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
> > - if (vring_mapping_error(vq, addr))
> > - goto unmap_release;
> > -
> > prev = i;
> > /* Note that we trust indirect descriptor
> > * table since it use stream DMA mapping.
> > */
> > - i = virtqueue_add_desc_split(_vq, desc, i, addr, sg->length,
> > + i = virtqueue_add_desc_split(_vq, desc, i,
> > + sg->dma_address,
> > + sg->length,
> > VRING_DESC_F_NEXT,
> > indirect);
> > }
> > }
> > for (; n < (out_sgs + in_sgs); n++) {
> > for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > - dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
> > - if (vring_mapping_error(vq, addr))
> > - goto unmap_release;
> > -
> > prev = i;
> > /* Note that we trust indirect descriptor
> > * table since it use stream DMA mapping.
> > */
> > - i = virtqueue_add_desc_split(_vq, desc, i, addr,
> > + i = virtqueue_add_desc_split(_vq, desc, i,
> > + sg->dma_address,
> > sg->length,
> > VRING_DESC_F_NEXT |
> > VRING_DESC_F_WRITE,
> > @@ -679,22 +748,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > return 0;
> >
> > unmap_release:
> > - err_idx = i;
> > -
> > - if (indirect)
> > - i = 0;
> > - else
> > - i = head;
> > -
> > - for (n = 0; n < total_sg; n++) {
> > - if (i == err_idx)
> > - break;
> > - if (indirect) {
> > - 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);
> > - }
> > + virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
> >
> > if (indirect)
> > kfree(desc);
> > --
> > 2.32.0.3.g01195cf9f
> >
>
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