netdev - Re: [PATCH vhost v13 11/12] virtio_ring: introduce dma sync api for virtqueue

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Date: Thu, 30 Nov 2023 18:15:55 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: virtualization@...ts.linux-foundation.org,
 Jason Wang <jasowang@...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>,
 netdev@...r.kernel.org,
 bpf@...r.kernel.org,
 Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH vhost v13 11/12] virtio_ring: introduce dma sync api for virtqueue

On Thu, 30 Nov 2023 05:10:42 -0500, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Thu, Nov 30, 2023 at 05:49:38PM +0800, Xuan Zhuo wrote:
> > On Thu, 30 Nov 2023 04:45:58 -0500, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> > > On Thu, Aug 10, 2023 at 08:30:56PM +0800, Xuan Zhuo wrote:
> > > > These API has been introduced:
> > > >
> > > > * virtqueue_dma_need_sync
> > > > * virtqueue_dma_sync_single_range_for_cpu
> > > > * virtqueue_dma_sync_single_range_for_device
> > > >
> > > > These APIs can be used together with the premapped mechanism to sync the
> > > > DMA address.
> > > >
> > > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > > ---
> > > >  drivers/virtio/virtio_ring.c | 76 ++++++++++++++++++++++++++++++++++++
> > > >  include/linux/virtio.h       |  8 ++++
> > > >  2 files changed, 84 insertions(+)
> > > >
> > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > index 916479c9c72c..81ecb29c88f1 100644
> > > > --- a/drivers/virtio/virtio_ring.c
> > > > +++ b/drivers/virtio/virtio_ring.c
> > > > @@ -3175,4 +3175,80 @@ int virtqueue_dma_mapping_error(struct virtqueue *_vq, dma_addr_t addr)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(virtqueue_dma_mapping_error);
> > > >
> > > > +/**
> > > > + * virtqueue_dma_need_sync - check a dma address needs sync
> > > > + * @_vq: the struct virtqueue we're talking about.
> > > > + * @addr: DMA address
> > > > + *
> > > > + * Check if the dma address mapped by the virtqueue_dma_map_* APIs needs to be
> > > > + * synchronized
> > > > + *
> > > > + * return bool
> > > > + */
> > > > +bool virtqueue_dma_need_sync(struct virtqueue *_vq, dma_addr_t addr)
> > > > +{
> > > > +	struct vring_virtqueue *vq = to_vvq(_vq);
> > > > +
> > > > +	if (!vq->use_dma_api)
> > > > +		return false;
> > > > +
> > > > +	return dma_need_sync(vring_dma_dev(vq), addr);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(virtqueue_dma_need_sync);
> > > > +
> > > > +/**
> > > > + * virtqueue_dma_sync_single_range_for_cpu - dma sync for cpu
> > > > + * @_vq: the struct virtqueue we're talking about.
> > > > + * @addr: DMA address
> > > > + * @offset: DMA address offset
> > > > + * @size: buf size for sync
> > > > + * @dir: DMA direction
> > > > + *
> > > > + * Before calling this function, use virtqueue_dma_need_sync() to confirm that
> > > > + * the DMA address really needs to be synchronized
> > > > + *
> > > > + */
> > > > +void virtqueue_dma_sync_single_range_for_cpu(struct virtqueue *_vq,
> > > > +					     dma_addr_t addr,
> > > > +					     unsigned long offset, size_t size,
> > > > +					     enum dma_data_direction dir)
> > > > +{
> > > > +	struct vring_virtqueue *vq = to_vvq(_vq);
> > > > +	struct device *dev = vring_dma_dev(vq);
> > > > +
> > > > +	if (!vq->use_dma_api)
> > > > +		return;
> > > > +
> > > > +	dma_sync_single_range_for_cpu(dev, addr, offset, size,
> > > > +				      DMA_BIDIRECTIONAL);
> > > > +}
> > >
> > >
> > > Why did you use DMA_BIDIRECTIONAL here?
> > > Why is "dir" ignored?
> >
> > This is a mistake.
> >
> > I see Jason has a fix patch.
>
> the one he sent in response to the bug report? it's incomplete though.
>
> > How can I help?
> >
> > Thanks.
>
> develop a full patch with commit log, explanation of what
> the result of the bug is, Fixes tag etc, test
> in some environment where dir makes a difference and post.

I'm ok.

Thanks


>
>
> >
> > >
> > >
> > > > +EXPORT_SYMBOL_GPL(virtqueue_dma_sync_single_range_for_cpu);
> > > > +
> > > > +/**
> > > > + * virtqueue_dma_sync_single_range_for_device - dma sync for device
> > > > + * @_vq: the struct virtqueue we're talking about.
> > > > + * @addr: DMA address
> > > > + * @offset: DMA address offset
> > > > + * @size: buf size for sync
> > > > + * @dir: DMA direction
> > > > + *
> > > > + * Before calling this function, use virtqueue_dma_need_sync() to confirm that
> > > > + * the DMA address really needs to be synchronized
> > > > + */
> > > > +void virtqueue_dma_sync_single_range_for_device(struct virtqueue *_vq,
> > > > +						dma_addr_t addr,
> > > > +						unsigned long offset, size_t size,
> > > > +						enum dma_data_direction dir)
> > > > +{
> > > > +	struct vring_virtqueue *vq = to_vvq(_vq);
> > > > +	struct device *dev = vring_dma_dev(vq);
> > > > +
> > > > +	if (!vq->use_dma_api)
> > > > +		return;
> > > > +
> > > > +	dma_sync_single_range_for_device(dev, addr, offset, size,
> > > > +					 DMA_BIDIRECTIONAL);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(virtqueue_dma_sync_single_range_for_device);
> > > > +
> > > >  MODULE_LICENSE("GPL");
> > >
> > > same question here.
> > >
> > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > > index 79e3c74391e0..1311a7fbe675 100644
> > > > --- a/include/linux/virtio.h
> > > > +++ b/include/linux/virtio.h
> > > > @@ -220,4 +220,12 @@ void virtqueue_dma_unmap_single_attrs(struct virtqueue *_vq, dma_addr_t addr,
> > > >  				      size_t size, enum dma_data_direction dir,
> > > >  				      unsigned long attrs);
> > > >  int virtqueue_dma_mapping_error(struct virtqueue *_vq, dma_addr_t addr);
> > > > +
> > > > +bool virtqueue_dma_need_sync(struct virtqueue *_vq, dma_addr_t addr);
> > > > +void virtqueue_dma_sync_single_range_for_cpu(struct virtqueue *_vq, dma_addr_t addr,
> > > > +					     unsigned long offset, size_t size,
> > > > +					     enum dma_data_direction dir);
> > > > +void virtqueue_dma_sync_single_range_for_device(struct virtqueue *_vq, dma_addr_t addr,
> > > > +						unsigned long offset, size_t size,
> > > > +						enum dma_data_direction dir);
> > > >  #endif /* _LINUX_VIRTIO_H */
> > > > --
> > > > 2.32.0.3.g01195cf9f
> > >
> > >
>