Re: [PATCH vhost v10 04/10] virtio_ring: packed: support add premapped buf

From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
To: Jason Wang <jasowang@redhat.com>
Cc: virtualization@lists.linux-foundation.org,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH vhost v10 04/10] virtio_ring: packed: support add premapped buf
Date: Tue, 27 Jun 2023 17:05:38 +0800	[thread overview]
Message-ID: <1687856738.178093-6-xuanzhuo@linux.alibaba.com> (raw)
In-Reply-To: <CACGkMEuoBtQ+=kJJk84Vs2sk7WAdh8O3d2wJLM-yBFAtkgLEUA@mail.gmail.com>

On Tue, 27 Jun 2023 16:03:29 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Fri, Jun 2, 2023 at 5:22 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > If the vq is the premapped mode, use the sg_dma_address() directly.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >  drivers/virtio/virtio_ring.c | 36 ++++++++++++++++++++++++++----------
> >  1 file changed, 26 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 18212c3e056b..dc109fbc05a5 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -1299,9 +1299,13 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> >
> >         for (n = 0; n < out_sgs + in_sgs; n++) {
> >                 for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> > -                       if (vring_map_one_sg(vq, sg, n < out_sgs ?
> > -                                            DMA_TO_DEVICE : DMA_FROM_DEVICE, &addr))
> > -                               goto unmap_release;
> > +                       if (vq->premapped) {
> > +                               addr = sg_dma_address(sg);
> > +                       } else {
> > +                               if (vring_map_one_sg(vq, sg, n < out_sgs ?
> > +                                                    DMA_TO_DEVICE : DMA_FROM_DEVICE, &addr))
> > +                                       goto unmap_release;
> > +                       }
> >
> >                         desc[i].flags = cpu_to_le16(n < out_sgs ?
> >                                                 0 : VRING_DESC_F_WRITE);
> > @@ -1369,10 +1373,12 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> >         return 0;
> >
> >  unmap_release:
> > -       err_idx = i;
> > +       if (!vq->premapped) {
> > +               err_idx = i;
> >
> > -       for (i = 0; i < err_idx; i++)
> > -               vring_unmap_desc_packed(vq, &desc[i]);
> > +               for (i = 0; i < err_idx; i++)
> > +                       vring_unmap_desc_packed(vq, &desc[i]);
> > +       }
> >
> >         kfree(desc);
> >
> > @@ -1447,9 +1453,13 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> >                 for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> >                         dma_addr_t addr;
> >
> > -                       if (vring_map_one_sg(vq, sg, n < out_sgs ?
> > -                                            DMA_TO_DEVICE : DMA_FROM_DEVICE, &addr))
> > -                               goto unmap_release;
> > +                       if (vq->premapped) {
> > +                               addr = sg_dma_address(sg);
> > +                       } else {
> > +                               if (vring_map_one_sg(vq, sg, n < out_sgs ?
> > +                                                    DMA_TO_DEVICE : DMA_FROM_DEVICE, &addr))
> > +                                       goto unmap_release;
> > +                       }
> >
> >                         flags = cpu_to_le16(vq->packed.avail_used_flags |
> >                                     (++c == total_sg ? 0 : VRING_DESC_F_NEXT) |
> > @@ -1512,11 +1522,17 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> >         return 0;
> >
> >  unmap_release:
> > +       vq->packed.avail_used_flags = avail_used_flags;
> > +
> > +       if (vq->premapped) {
>
> Similar to the split path, I think we can't hit vq->premapped here.

YES, similar to the above reply, we can have a better way.

But, we can hit vq->premapped, when we fail doing dma for the indirect desc
array.

Thanks.

>
> Thanks
>
>
> > +               END_USE(vq);
> > +               return -EIO;
> > +       }
> > +
> >         err_idx = i;
> >         i = head;
> >         curr = vq->free_head;
> >
> > -       vq->packed.avail_used_flags = avail_used_flags;
> >
> >         for (n = 0; n < total_sg; n++) {
> >                 if (i == err_idx)
> > --
> > 2.32.0.3.g01195cf9f
> >
>