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?).
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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