On Thu, Oct 12, 2023 at 05:18:54PM +0800, Xuan Zhuo wrote:
> On Thu, 12 Oct 2023 05:15:52 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > On Wed, Oct 11, 2023 at 05:27:07PM +0800, Xuan Zhuo wrote:
> > > virtqueue_set_dma_premapped() adds a new parameter to disable the
> > > virtqueue premapped mode.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > ---
> > > drivers/net/virtio_net.c | 2 +-
> > > drivers/virtio/virtio_ring.c | 11 ++++++++---
> > > include/linux/virtio.h | 2 +-
> > > 3 files changed, 10 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index fe7f314d65c9..6b5f47ebf9b2 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -737,7 +737,7 @@ static void virtnet_rq_set_premapped(struct virtnet_info *vi)
> > > return;
> > >
> > > for (i = 0; i < vi->max_queue_pairs; i++) {
> > > - if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> > > + if (virtqueue_set_dma_premapped(vi->rq[i].vq, true))
> > > continue;
> > >
> > > vi->rq[i].do_dma = true;
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 51d8f3299c10..b3ded56722f4 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -2784,7 +2784,7 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
> > > * 0: success.
> > > * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
> > > */
> > > -int virtqueue_set_dma_premapped(struct virtqueue *_vq)
> > > +int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool mode)
> > > {
> > > struct vring_virtqueue *vq = to_vvq(_vq);
> > > u32 num;
> > > @@ -2803,8 +2803,13 @@ int virtqueue_set_dma_premapped(struct virtqueue *_vq)
> > > return -EINVAL;
> > > }
> > >
> > > - vq->premapped = true;
> > > - vq->do_unmap = false;
> > > + if (mode) {
> > > + vq->premapped = true;
> > > + vq->do_unmap = false;
> > > + } else {
> > > + vq->premapped = false;
> > > + vq->do_unmap = vq->use_dma_api;
> > > + }
> > >
> > > END_USE(vq);
> > >
> > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > index 4cc614a38376..1cf7b004348b 100644
> > > --- a/include/linux/virtio.h
> > > +++ b/include/linux/virtio.h
> > > @@ -81,7 +81,7 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
> > >
> > > unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
> > >
> > > -int virtqueue_set_dma_premapped(struct virtqueue *_vq);
> > > +int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool mode);
> > >
> > > bool virtqueue_poll(struct virtqueue *vq, unsigned);
> >
> > Wait a sec I thought we never change premapped. If you make this
> > dynamic don't you need a bunch of locking?
> > Or maybe queue is empty when you change this?
> > If yes pls add a bunch of BUG_ON checks to make sure this is not misused.
>
>
> Actually, this api is called immediately after the vq init or vq reset.
>
> We already have such a check.
>
> Thanks.
>
> /**
> * virtqueue_set_dma_premapped - set the vring premapped mode
> * @_vq: the struct virtqueue we're talking about.
> *
> * Enable the premapped mode of the vq.
> *
> * The vring in premapped mode does not do dma internally, so the driver must
> * do dma mapping in advance. The driver must pass the dma_address through
> * dma_address of scatterlist. When the driver got a used buffer from
> * the vring, it has to unmap the dma address.
> *
> * This function must be called immediately after creating the vq, or after vq
> * reset, and before adding any buffers to it.
> *
> * Caller must ensure we don't call this with other virtqueue operations
> * at the same time (except where noted).
> *
> * Returns zero or a negative error.
> * 0: success.
> * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
> */
> int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool mode)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> u32 num;
>
> START_USE(vq);
>
> num = vq->packed_ring ? vq->packed.vring.num : vq->split.vring.num;
>
> --> if (num != vq->vq.num_free) {
> END_USE(vq);
> return -EINVAL;
> }
But it turns out virtnet_rq_set_premapped actually just ignores errors.
So returning EINVAL here does nothing caller just proceeds?
And checking num_free without locks is never safe anyway.
I think the point is that this never triggers then just BUG_ON.
>
> if (!vq->use_dma_api) {
> END_USE(vq);
> return -EINVAL;
> }
>
> if (mode) {
> vq->premapped = true;
> vq->do_unmap = false;
> } else {
> vq->premapped = false;
> vq->do_unmap = vq->use_dma_api;
> }
>
> END_USE(vq);
>
> return 0;
> }
> EXPORT_SYMBOL_GPL(virtqueue_set_dma_premapped);
>
>
> >
> >
> > > --
> > > 2.32.0.3.g01195cf9f
> >
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