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Message-ID: <1727166724.3220332-2-xuanzhuo@linux.alibaba.com>
Date: Tue, 24 Sep 2024 16:32:04 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org,
"Michael S. Tsirkin" <mst@...hat.com>,
Eugenio Pérez <eperezma@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
virtualization@...ts.linux.dev,
bpf@...r.kernel.org
Subject: Re: [RFC net-next v1 02/12] virtio_ring: split: record extras for indirect buffers
Will fix for all commets in next version.
Thanks.
On Tue, 24 Sep 2024 15:34:57 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Tue, Sep 24, 2024 at 9:32 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > The subsequent commit needs to know whether every indirect buffer is
> > premapped or not. So we need to introduce an extra struct for every
> > indirect buffer to record this info.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> > drivers/virtio/virtio_ring.c | 126 +++++++++++++++++------------------
> > 1 file changed, 61 insertions(+), 65 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 228e9fbcba3f..62901bee97c0 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -67,9 +67,20 @@
> > #define LAST_ADD_TIME_INVALID(vq)
> > #endif
> >
> > +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. */
> > +};
> > +
> > struct vring_desc_state_split {
> > void *data; /* Data for callback. */
> > - struct vring_desc *indir_desc; /* Indirect descriptor, if any. */
> > +
> > + /* Indirect extra table and desc table, if any. These two will be
> > + * allocated together. So we won't stress more to the memory allocator.
> > + */
> > + struct vring_desc_extra *indir;
> > };
> >
> > struct vring_desc_state_packed {
> > @@ -79,13 +90,6 @@ struct vring_desc_state_packed {
> > u16 last; /* The last desc state in a list. */
> > };
> >
> > -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. */
> > -};
> > -
> > struct vring_virtqueue_split {
> > /* Actual memory layout for this queue. */
> > struct vring vring;
> > @@ -440,38 +444,20 @@ static void virtqueue_init(struct vring_virtqueue *vq, u32 num)
> > * Split ring specific functions - *_split().
> > */
> >
> > -static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
> > - const struct vring_desc *desc)
> > -{
> > - u16 flags;
> > -
> > - if (!vring_need_unmap_buffer(vq))
> > - return;
> > -
> > - flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
> > -
> > - dma_unmap_page(vring_dma_dev(vq),
> > - virtio64_to_cpu(vq->vq.vdev, desc->addr),
> > - virtio32_to_cpu(vq->vq.vdev, desc->len),
> > - (flags & VRING_DESC_F_WRITE) ?
> > - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> > -}
> > -
> > static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> > - unsigned int i)
> > + struct vring_desc_extra *extra)
> > {
> > - struct vring_desc_extra *extra = vq->split.desc_extra;
> > u16 flags;
> >
> > - flags = extra[i].flags;
> > + flags = extra->flags;
> >
> > if (flags & VRING_DESC_F_INDIRECT) {
> > if (!vq->use_dma_api)
> > goto out;
> >
> > dma_unmap_single(vring_dma_dev(vq),
> > - extra[i].addr,
> > - extra[i].len,
> > + extra->addr,
> > + extra->len,
> > (flags & VRING_DESC_F_WRITE) ?
> > DMA_FROM_DEVICE : DMA_TO_DEVICE);
> > } else {
> > @@ -479,20 +465,22 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
> > goto out;
> >
> > dma_unmap_page(vring_dma_dev(vq),
> > - extra[i].addr,
> > - extra[i].len,
> > + extra->addr,
> > + extra->len,
> > (flags & VRING_DESC_F_WRITE) ?
> > DMA_FROM_DEVICE : DMA_TO_DEVICE);
> > }
> >
> > out:
> > - return extra[i].next;
> > + return extra->next;
> > }
> >
> > static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
> > unsigned int total_sg,
> > + struct vring_desc_extra **pextra,
>
> This kind of API seems a little bit strange. In the caller we had:
>
> if (desc) {
> ...
> } else {
> extra = vq->split.desc_extra;
> }
>
> I'd move the assignment of the extra there to make the code more readable.
>
> > gfp_t gfp)
> > {
> > + struct vring_desc_extra *extra;
> > struct vring_desc *desc;
> > unsigned int i;
> >
> > @@ -503,40 +491,45 @@ static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
> > */
> > gfp &= ~__GFP_HIGHMEM;
> >
> > - desc = kmalloc_array(total_sg, sizeof(struct vring_desc), gfp);
> > - if (!desc)
> > + extra = kmalloc_array(total_sg, sizeof(*desc) + sizeof(*extra), gfp);
>
> I'd suggest using kmalloc() directly, as it seems not an array where
> each descriptor is followed by one extra.
>
> > + if (!extra)
> > return NULL;
> >
> > - for (i = 0; i < total_sg; i++)
> > + desc = (struct vring_desc *)&extra[total_sg];
>
> Still seems strange, I would rather make the descriptor come first
> then. This makes code more readable. And we can keep the indir_desc
> variable name.
>
> > +
> > + for (i = 0; i < total_sg; i++) {
> > desc[i].next = cpu_to_virtio16(_vq->vdev, i + 1);
> > + extra[i].next = i + 1;
> > + }
> > +
> > + *pextra = extra;
> > +
> > return desc;
> > }
> >
> > static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
> > struct vring_desc *desc,
> > + struct vring_desc_extra *extra,
> > unsigned int i,
> > dma_addr_t addr,
> > unsigned int len,
> > u16 flags,
> > bool indirect)
> > {
> > - struct vring_virtqueue *vring = to_vvq(vq);
> > - struct vring_desc_extra *extra = vring->split.desc_extra;
> > u16 next;
> >
> > desc[i].flags = cpu_to_virtio16(vq->vdev, flags);
> > desc[i].addr = cpu_to_virtio64(vq->vdev, addr);
> > desc[i].len = cpu_to_virtio32(vq->vdev, len);
> >
> > - if (!indirect) {
> > - next = extra[i].next;
> > - desc[i].next = cpu_to_virtio16(vq->vdev, next);
> > + extra[i].addr = addr;
> > + extra[i].len = len;
> > + extra[i].flags = flags;
> > +
> > + next = extra[i].next;
> >
> > - extra[i].addr = addr;
> > - extra[i].len = len;
> > - extra[i].flags = flags;
> > - } else
> > - next = virtio16_to_cpu(vq->vdev, desc[i].next);
> > + if (!indirect)
> > + desc[i].next = cpu_to_virtio16(vq->vdev, next);
>
> Any chance we can remove the check for indirect here? For example,
> remove the assignment in alloc_indirect_split(). This would be more
> consistent with the way when we want to use desc_extra for both
> indirect and direct descriptors.
>
> >
> > return next;
> > }
> > @@ -551,6 +544,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > gfp_t gfp)
> > {
> > struct vring_virtqueue *vq = to_vvq(_vq);
> > + struct vring_desc_extra *extra;
> > struct scatterlist *sg;
> > struct vring_desc *desc;
> > unsigned int i, n, avail, descs_used, prev, err_idx;
> > @@ -574,7 +568,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > head = vq->free_head;
> >
> > if (virtqueue_use_indirect(vq, total_sg))
> > - desc = alloc_indirect_split(_vq, total_sg, gfp);
> > + desc = alloc_indirect_split(_vq, total_sg, &extra, gfp);
> > else {
> > desc = NULL;
> > WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
> > @@ -589,6 +583,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > } else {
> > indirect = false;
> > desc = vq->split.vring.desc;
> > + extra = vq->split.desc_extra;
> > i = head;
> > descs_used = total_sg;
> > }
> > @@ -618,7 +613,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > /* 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, extra, i, addr, sg->length,
> > VRING_DESC_F_NEXT,
> > indirect);
> > }
> > @@ -634,7 +629,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > /* 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, extra, i, addr,
> > sg->length,
> > VRING_DESC_F_NEXT |
> > VRING_DESC_F_WRITE,
> > @@ -660,6 +655,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > }
> >
> > virtqueue_add_desc_split(_vq, vq->split.vring.desc,
> > + vq->split.desc_extra,
> > head, addr,
> > total_sg * sizeof(struct vring_desc),
> > VRING_DESC_F_INDIRECT,
> > @@ -678,9 +674,9 @@ 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 = extra;
> > else
> > - vq->split.desc_state[head].indir_desc = ctx;
> > + vq->split.desc_state[head].indir = ctx;
> >
> > /* Put entry in available array (but don't update avail->idx until they
> > * do sync). */
> > @@ -716,11 +712,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > 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);
> > +
> > + i = vring_unmap_one_split(vq, &extra[i]);
> > }
> >
> > free_indirect:
> > @@ -765,22 +758,25 @@ static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
> > static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> > void **ctx)
> > {
> > + struct vring_desc_extra *extra;
> > unsigned int i, j;
> > __virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
> >
> > /* Clear data ptr. */
> > vq->split.desc_state[head].data = NULL;
> >
> > + extra = vq->split.desc_extra;
> > +
> > /* Put back on free list: unmap first-level descriptors and find end */
> > i = head;
> >
> > while (vq->split.vring.desc[i].flags & nextflag) {
> > - vring_unmap_one_split(vq, i);
> > + vring_unmap_one_split(vq, &extra[i]);
> > i = vq->split.desc_extra[i].next;
> > vq->vq.num_free++;
> > }
> >
> > - vring_unmap_one_split(vq, i);
> > + vring_unmap_one_split(vq, &extra[i]);
> > vq->split.desc_extra[i].next = vq->free_head;
> > vq->free_head = head;
> >
> > @@ -788,12 +784,12 @@ 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;
> > u32 len;
> >
> > + extra = vq->split.desc_state[head].indir;
> > +
> > /* Free the indirect table, if any, now that it's unmapped. */
> > - if (!indir_desc)
> > + if (!extra)
> > return;
> >
> > len = vq->split.desc_extra[head].len;
> > @@ -804,13 +800,13 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> >
> > if (vring_need_unmap_buffer(vq)) {
> > for (j = 0; j < len / sizeof(struct vring_desc); j++)
> > - vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> > + vring_unmap_one_split(vq, &extra[j]);
> > }
> >
> > - kfree(indir_desc);
> > - vq->split.desc_state[head].indir_desc = NULL;
> > + kfree(extra);
> > + vq->split.desc_state[head].indir = NULL;
> > } else if (ctx) {
> > - *ctx = vq->split.desc_state[head].indir_desc;
> > + *ctx = vq->split.desc_state[head].indir;
> > }
> > }
> >
> > --
> > 2.32.0.3.g01195cf9f
> >
>
> Thanks
>
>
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