On Wed, 15 Mar 2023 12:47:29 +0800, Jason Wang <jasow...@redhat.com> wrote:
> On Tue, Mar 14, 2023 at 5:17 PM Xuan Zhuo <xuanz...@linux.alibaba.com> wrote:
> >
> > On Tue, 14 Mar 2023 15:57:06 +0800, Jason Wang <jasow...@redhat.com> wrote:
> > > On Wed, Mar 8, 2023 at 2:44 PM Xuan Zhuo <xuanz...@linux.alibaba.com>
> > > wrote:
> > > >
> > > > virtio core only supports virtual addresses, dma is completed in virtio
> > > > core.
> > > >
> > > > In some scenarios (such as the AF_XDP), the memory is allocated
> > > > and DMA is completed in advance, so it is necessary for us to support
> > > > passing the DMA address to virtio core.
> > > >
> > > > Drives can use sg->dma_address to pass the mapped dma address to virtio
> > > > core. If one sg->dma_address is used then all sgs must use
> > > > sg->dma_address,
> > > > otherwise all dma_address must be null.
> > > >
> > > > On the indirect path, if dma_address is used, desc_state.indir_desc will
> > > > be mixed with VRING_INDIRECT_PREMAPPED. So when do unmap, we can pass
> > > > it.
> > >
> > > It's better to mention why indirect descriptors can't be done in the
> > > same way with direct descriptors.
> > >
> > > Btw, if we change the semantics of desc_extra.dma_addr and
> > > desc_state.indir_desc, we should add comments to definitions of those
> > > structures.
> >
> >
> > Will fix.
> >
> > >
> > > >
> > > > Signed-off-by: Xuan Zhuo <xuanz...@linux.alibaba.com>
> > > > ---
> > > > drivers/virtio/virtio_ring.c | 28 ++++++++++++++++++++++------
> > > > 1 file changed, 22 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > index 66a071e3bdef..11827d2e56a8 100644
> > > > --- a/drivers/virtio/virtio_ring.c
> > > > +++ b/drivers/virtio/virtio_ring.c
> > > > @@ -231,6 +231,18 @@ static void vring_free(struct virtqueue *_vq);
> > > > * Helpers.
> > > > */
> > > >
> > > > +#define VRING_INDIRECT_PREMAPPED BIT(0)
> > > > +
> > > > +#define desc_mix_dma_map(do_map, desc) \
> > > > + (do_map ? desc : (typeof(desc))((unsigned long)(desc) |
> > > > VRING_INDIRECT_PREMAPPED))
> > > > +
> > > > +#define desc_rm_dma_map(desc) \
> > > > + ((typeof(desc))((unsigned long)(desc) &
> > > > ~VRING_INDIRECT_PREMAPPED))
> > > > +
> > > > +#define desc_map_inter(desc) \
> > > > + !((unsigned long)(desc) & VRING_INDIRECT_PREMAPPED)
> > > > +
> > > > +
> > > > #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
> > > >
> > > > static inline bool virtqueue_use_indirect(struct vring_virtqueue *vq,
> > > > @@ -725,7 +737,7 @@ static inline int virtqueue_add_split(struct
> > > > virtqueue *_vq,
> > > > /* Store token and indirect buffer state. */
> > > > vq->split.desc_state[head].data = data;
> > > > if (indirect)
> > > > - vq->split.desc_state[head].indir_desc = desc;
> > > > + vq->split.desc_state[head].indir_desc =
> > > > desc_mix_dma_map(do_map, desc);
> > >
> > > So using indir_desc is kind of hacky (since we don't use indirect for
> > > rx with extra context).
> > >
> > > But at least I think we should seeka way to use the same metadata for
> > > both direct and indirect descriptors.
> > >
> > > E.g can we make them all to use indir_desc?
> >
> > I think it may not. My original idea is to use indir_desc uniformly, but
> > for the scene of saving ctx, we cannot guarantee that the ctx has space for
> > us.
>
> Ok, but the problem is that the code became even more hacky (imagine
> one day we may want to use indirect for RX?).
I think it may have nothing to do with RX, but whether ctx is used. Because ctx
and indirect cannot coexist.
static inline int virtqueue_add_split(struct virtqueue *_vq,
struct scatterlist *sgs[],
unsigned int total_sg,
unsigned int out_sgs,
unsigned int in_sgs,
void *data,
void *ctx,
gfp_t gfp)
{
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;
bool indirect;
START_USE(vq);
BUG_ON(data == NULL);
> BUG_ON(ctx && vq->indirect);
If we want to use ctx with indirect, we must add an dedicated metadata for ctx.
So I think the current plan is OK.
Thanks.
>
> So I tend to change my mind to introduce dedicated metadata, instead
> of trying to be packed with two types of the existing ones.
>
> Thanks
>
> >
> > Thanks.
> >
> > >
> > > Thanks
> > >
> > > > else
> > > > vq->split.desc_state[head].indir_desc = ctx;
> > > >
> > > > @@ -820,22 +832,26 @@ static void detach_buf_split(struct
> > > > vring_virtqueue *vq, unsigned int head,
> > > > vq->vq.num_free++;
> > > >
> > > > if (vq->indirect) {
> > > > - struct vring_desc *indir_desc =
> > > > - vq->split.desc_state[head].indir_desc;
> > > > + struct vring_desc *mix =
> > > > vq->split.desc_state[head].indir_desc;
> > > > + struct vring_desc *indir_desc;
> > > > u32 len;
> > > >
> > > > /* Free the indirect table, if any, now that it's
> > > > unmapped. */
> > > > - if (!indir_desc)
> > > > + if (!mix)
> > > > return;
> > > >
> > > > + indir_desc = desc_rm_dma_map(mix);
> > > > +
> > > > len = vq->split.desc_extra[head].len;
> > > >
> > > > BUG_ON(!(vq->split.desc_extra[head].flags &
> > > > VRING_DESC_F_INDIRECT));
> > > > BUG_ON(len == 0 || len % sizeof(struct vring_desc));
> > > >
> > > > - for (j = 0; j < len / sizeof(struct vring_desc); j++)
> > > > - vring_unmap_one_split_indirect(vq,
> > > > &indir_desc[j]);
> > > > + if (desc_map_inter(mix)) {
> > > > + for (j = 0; j < len / sizeof(struct
> > > > vring_desc); j++)
> > > > + vring_unmap_one_split_indirect(vq,
> > > > &indir_desc[j]);
> > > > + }
> > > >
> > > > kfree(indir_desc);
> > > > vq->split.desc_state[head].indir_desc = NULL;
> > > > --
> > > > 2.32.0.3.g01195cf9f
> > > >
> > >
> >
>
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