On Tue, Nov 21, 2023 at 2:27 PM Xuan Zhuo <[email protected]> wrote:
>
> On Thu, 16 Nov 2023 16:11:11 +0800, Jason Wang <[email protected]> wrote:
> > On Tue, Nov 14, 2023 at 7:31 PM Xuan Zhuo <[email protected]>
> > wrote:
> > >
> > > introduce virtqueue_get_buf_ctx_dma() to collect the dma info when
> > > get buf from virtio core for premapped mode.
> > >
> > > If the virtio queue is premapped mode, the virtio-net send buf may
> > > have many desc. Every desc dma address need to be unmap. So here we
> > > introduce a new helper to collect the dma address of the buffer from
> > > the virtio core.
> >
> > So looking at vring_desc_extra, what we have right now is:
> >
> > struct vring_desc_extra {
> > dma_addr_t addr; /* Descriptor DMA addr. */
> > u32 len; /* Descriptor length. */
> > u16 flags; /* Descriptor flags. */
> > u16 next; /* The next desc state in a list. */
> > };
> >
> > And sg is
> >
> > struct scatterlist {
> > unsigned long page_link;
> > unsigned int offset;
> > unsigned int length;
> > dma_addr_t dma_address;
> > #ifdef CONFIG_NEED_SG_DMA_LENGTH
> > unsigned int dma_length;
> > #endif
> > #ifdef CONFIG_NEED_SG_DMA_FLAGS
> > unsigned int dma_flags;
> > #endif
> > };
> >
> > Would it better just store sg?
>
> Do you mean we expose the vring_desc_extra to dirver?
Maybe or not, (or just us sg for desc_extra).
Anyhow, any method needs to be benchmarked to see the performance impact.
>
> How about introducing such a new structure?
>
> struct virtio_dma_item {
> dma_addr_t addr;
> u32 len;
> };
>
> struct virtio_dma_head {
> u32 num;
> u32 used;
> struct virtio_dma_item items[];
> };
>
> Then we just need to pass one pointer to the virtio.
Just to make sure I understand here, where did we store those arrays?
> num is used to pass the size of items
> used is used to return the num used by virtio core.
>
> >
> > More below
> >
> > >
> > > Signed-off-by: Xuan Zhuo <[email protected]>
> > > ---
> > > drivers/virtio/virtio_ring.c | 148 ++++++++++++++++++++++++++---------
> > > include/linux/virtio.h | 2 +
> > > 2 files changed, 115 insertions(+), 35 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 51d8f3299c10..0b3caee4ef9d 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -362,6 +362,20 @@ static struct device *vring_dma_dev(const struct
> > > vring_virtqueue *vq)
> > > return vq->dma_dev;
> > > }
> > >
> > > +static void store_dma_to_sg(struct scatterlist **sgp, dma_addr_t addr,
> > > unsigned int length)
> > > +{
> > > + struct scatterlist *sg;
> > > +
> > > + sg = *sgp;
> > > +
> > > + sg->dma_address = addr;
> > > + sg->length = length;
> > > +
> > > + sg = sg_next(sg);
> > > +
> > > + *sgp = sg;
> > > +}
> > > +
> > > /* Map one sg entry. */
> > > static int vring_map_one_sg(const struct vring_virtqueue *vq, struct
> > > scatterlist *sg,
> > > enum dma_data_direction direction, dma_addr_t
> > > *addr)
> > > @@ -441,12 +455,18 @@ static void virtqueue_init(struct vring_virtqueue
> > > *vq, u32 num)
> > > */
> > >
> > > static void vring_unmap_one_split_indirect(const struct vring_virtqueue
> > > *vq,
> > > - const struct vring_desc *desc)
> > > + const struct vring_desc *desc,
> > > + struct scatterlist **sg)
> > > {
> > > u16 flags;
> > >
> > > - if (!vq->do_unmap)
> > > + if (!vq->do_unmap) {
> > > + if (*sg)
> >
> > Can we simply move the
> >
> > if (*sg) to store_dma_to_sg()?
>
> OK
>
>
> >
> > > + store_dma_to_sg(sg,
> > > + virtio64_to_cpu(vq->vq.vdev,
> > > desc->addr),
> > > + virtio32_to_cpu(vq->vq.vdev,
> > > desc->len));
> > > return;
> > > + }
> > >
> > > flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
> > >
> > > @@ -458,7 +478,7 @@ 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, struct
> > > scatterlist **sg)
> > > {
> > > struct vring_desc_extra *extra = vq->split.desc_extra;
> > > u16 flags;
> > > @@ -475,8 +495,11 @@ 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 (!vq->do_unmap)
> > > + if (!vq->do_unmap) {
> >
> > The:
> >
> > else {
> > if {
> > if {
> > }
> >
> > seems odd. I think I would prefer
> >
> > if (flags & VRING_DESC_F_INDIRECT) {
> > } else if (!vq->do_unmap) {
> > } else {
> > }
>
>
> Will fix.
>
>
> >
> > here
> >
> > Btw, I really think do_unmap is not a good name, we probably need to
> > rename it as "unmap_desc".
>
> How about a separate patch for this?
>
> >
> >
> > > + if (*sg)
> > > + store_dma_to_sg(sg, extra[i].addr,
> > > extra[i].len);
> >
> > In which case we need to unmap by driver but we don't need a dma address?
>
> Sorry, do not get it.
I meant, I don't get how we can reach to this check.
>
> >
> > > goto out;
> > > + }
> > >
> > > dma_unmap_page(vring_dma_dev(vq),
> > > extra[i].addr,
> > > @@ -717,10 +740,10 @@ static inline int virtqueue_add_split(struct
> > > virtqueue *_vq,
> > > if (i == err_idx)
> > > break;
> > > if (indirect) {
> > > - vring_unmap_one_split_indirect(vq, &desc[i]);
> > > + vring_unmap_one_split_indirect(vq, &desc[i],
> > > NULL);
> > > i = virtio16_to_cpu(_vq->vdev, desc[i].next);
> > > } else
> > > - i = vring_unmap_one_split(vq, i);
> > > + i = vring_unmap_one_split(vq, i, NULL);
> > > }
> > >
> > > free_indirect:
> > > @@ -763,7 +786,7 @@ static bool virtqueue_kick_prepare_split(struct
> > > virtqueue *_vq)
> > > }
> > >
> > > static void detach_buf_split(struct vring_virtqueue *vq, unsigned int
> > > head,
> > > - void **ctx)
> > > + struct scatterlist *sg, void **ctx)
> > > {
> > > unsigned int i, j;
> > > __virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev,
> > > VRING_DESC_F_NEXT);
> > > @@ -775,12 +798,12 @@ 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, &sg);
> > > i = vq->split.desc_extra[i].next;
> > > vq->vq.num_free++;
> > > }
> > >
> > > - vring_unmap_one_split(vq, i);
> > > + vring_unmap_one_split(vq, i, &sg);
> > > vq->split.desc_extra[i].next = vq->free_head;
> > > vq->free_head = head;
> > >
> > > @@ -794,7 +817,7 @@ static void detach_buf_split(struct vring_virtqueue
> > > *vq, unsigned int head,
> > >
> > > /* Free the indirect table, if any, now that it's
> > > unmapped. */
> > > if (!indir_desc)
> > > - return;
> > > + goto end;
> > >
> > > len = vq->split.desc_extra[head].len;
> > >
> > > @@ -802,9 +825,10 @@ 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->do_unmap) {
> > > + if (vq->do_unmap || sg) {
> > > for (j = 0; j < len / sizeof(struct vring_desc);
> > > j++)
> > > - vring_unmap_one_split_indirect(vq,
> > > &indir_desc[j]);
> > > + vring_unmap_one_split_indirect(vq,
> > > &indir_desc[j], &sg);
> > > +
> > > }
> > >
> > > kfree(indir_desc);
> > > @@ -812,6 +836,11 @@ static void detach_buf_split(struct vring_virtqueue
> > > *vq, unsigned int head,
> > > } else if (ctx) {
> > > *ctx = vq->split.desc_state[head].indir_desc;
> > > }
> > > +
> > > +end:
> > > + /* sg point to the next. So we mark the last one as the end. */
> > > + if (!vq->do_unmap && sg)
> > > + sg_mark_end(sg - 1);
> > > }
> > >
> > > static bool more_used_split(const struct vring_virtqueue *vq)
> > > @@ -822,6 +851,7 @@ static bool more_used_split(const struct
> > > vring_virtqueue *vq)
> > >
> > > static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
> > > unsigned int *len,
> > > + struct scatterlist *sg,
> > > void **ctx)
> > > {
> > > struct vring_virtqueue *vq = to_vvq(_vq);
> > > @@ -862,7 +892,7 @@ static void *virtqueue_get_buf_ctx_split(struct
> > > virtqueue *_vq,
> > >
> > > /* detach_buf_split clears data, so grab it now. */
> > > ret = vq->split.desc_state[i].data;
> > > - detach_buf_split(vq, i, ctx);
> > > + detach_buf_split(vq, i, sg, ctx);
> > > vq->last_used_idx++;
> > > /* If we expect an interrupt for the next entry, tell host
> > > * by writing event index and flush out the write before
> > > @@ -984,7 +1014,7 @@ static void
> > > *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
> > > continue;
> > > /* detach_buf_split clears data, so grab it now. */
> > > buf = vq->split.desc_state[i].data;
> > > - detach_buf_split(vq, i, NULL);
> > > + detach_buf_split(vq, i, NULL, NULL);
> > > vq->split.avail_idx_shadow--;
> > > vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
> > > vq->split.avail_idx_shadow);
> > > @@ -1221,7 +1251,8 @@ static u16 packed_last_used(u16 last_used_idx)
> > > }
> > >
> > > static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
> > > - const struct vring_desc_extra *extra)
> > > + const struct vring_desc_extra *extra,
> > > + struct scatterlist **sg)
> > > {
> > > u16 flags;
> > >
> > > @@ -1236,8 +1267,11 @@ static void vring_unmap_extra_packed(const struct
> > > vring_virtqueue *vq,
> > > (flags & VRING_DESC_F_WRITE) ?
> > > DMA_FROM_DEVICE : DMA_TO_DEVICE);
> > > } else {
> > > - if (!vq->do_unmap)
> > > + if (!vq->do_unmap) {
> > > + if (*sg)
> > > + store_dma_to_sg(sg, extra->addr,
> > > extra->len);
> > > return;
> > > + }
> > >
> > > dma_unmap_page(vring_dma_dev(vq),
> > > extra->addr, extra->len,
> > > @@ -1247,12 +1281,17 @@ static void vring_unmap_extra_packed(const struct
> > > vring_virtqueue *vq,
> > > }
> > >
> > > static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
> > > - const struct vring_packed_desc *desc)
> > > + const struct vring_packed_desc *desc,
> > > + struct scatterlist **sg)
> > > {
> >
> > Interesting, I think this is only needed for indirect descriptors?
> >
> > If yes, why do we care about the dma addresses of indirect descriptors?
> > If not, it's a bug that we should use desc_extra, otherwise it's a
> > device-triggerable unmap which has security implications (we need to
> > use vring_extra in this case).
>
> Sorry, I do not get.
>
> indirect desc(alloc by virtio core)
> virtio-desc ------> | | -------------------------------------> dma
> address of buffer
> | | -------------------------------------> dma
> address of buffer
> | | -------------------------------------> dma
> address of buffer
> | | -------------------------------------> dma
> address of buffer
> | | -------------------------------------> dma
> address of buffer
> | | -------------------------------------> dma
> address of buffer
>
> For vring_unmap_desc_packed the desc is the indirect desc(alloc by virtio
> core,
> not the virtio desc), which record the dma address of buffer that is passed by
> the driver. Here we need to record the dma address to back to the driver.
I meant why should we return this to the driver? It is allocated by
the vitio core and should be transparent to the driver.
Thanks
