Jason Wang
2022-Feb-23 03:19 UTC
[PATCH] virtio_ring: aovid reading flag from the descriptor ring
On Mon, Nov 8, 2021 at 4:13 PM Jason Wang <jasowang at redhat.com> wrote:> > Commit 72b5e8958738 ("virtio-ring: store DMA metadata in desc_extra > for split virtqueue") tries to make it possible for the driver to not > read from the descriptor ring to prevent the device from corrupting > the descriptor ring. But it still read the descriptor flag from the > descriptor ring during buffer detach. > > This patch fixes by always store the descriptor flag no matter whether > DMA API is used and then we can avoid reading descriptor flag from the > descriptor ring. This eliminates the possibly of unexpected next > descriptor caused by the wrong flag (e.g the next flag). > > Signed-off-by: Jason Wang <jasowang at redhat.com>Michael, any comment for this? Thanks> --- > drivers/virtio/virtio_ring.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 00f64f2f8b72..28734f4e57d3 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -583,7 +583,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, > } > /* Last one doesn't continue. */ > desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); > - if (!indirect && vq->use_dma_api) > + if (!indirect) > vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &> ~VRING_DESC_F_NEXT; > > @@ -713,7 +713,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head, > /* Put back on free list: unmap first-level descriptors and find end */ > i = head; > > - while (vq->split.vring.desc[i].flags & nextflag) { > + while (vq->split.desc_extra[i].flags & nextflag) { > vring_unmap_one_split(vq, i); > i = vq->split.desc_extra[i].next; > vq->vq.num_free++; > -- > 2.25.1 >
Michael S. Tsirkin
2022-Feb-23 07:08 UTC
[PATCH] virtio_ring: aovid reading flag from the descriptor ring
On Wed, Feb 23, 2022 at 11:19:03AM +0800, Jason Wang wrote:> On Mon, Nov 8, 2021 at 4:13 PM Jason Wang <jasowang at redhat.com> wrote: > > > > Commit 72b5e8958738 ("virtio-ring: store DMA metadata in desc_extra > > for split virtqueue") tries to make it possible for the driver to not > > read from the descriptor ring to prevent the device from corrupting > > the descriptor ring. But it still read the descriptor flag from the > > descriptor ring during buffer detach. > > > > This patch fixes by always store the descriptor flag no matter whether > > DMA API is used and then we can avoid reading descriptor flag from the > > descriptor ring. This eliminates the possibly of unexpected next > > descriptor caused by the wrong flag (e.g the next flag). > > > > Signed-off-by: Jason Wang <jasowang at redhat.com> > > Michael, any comment for this? > > ThanksI don't exactly see why we should care without DMA API, it seems cleaner not to poke at the array one extra time.> > --- > > drivers/virtio/virtio_ring.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index 00f64f2f8b72..28734f4e57d3 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -583,7 +583,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, > > } > > /* Last one doesn't continue. */ > > desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); > > - if (!indirect && vq->use_dma_api) > > + if (!indirect) > > vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &> > ~VRING_DESC_F_NEXT; > > > > @@ -713,7 +713,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head, > > /* Put back on free list: unmap first-level descriptors and find end */ > > i = head; > > > > - while (vq->split.vring.desc[i].flags & nextflag) { > > + while (vq->split.desc_extra[i].flags & nextflag) { > > vring_unmap_one_split(vq, i); > > i = vq->split.desc_extra[i].next; > > vq->vq.num_free++; > > -- > > 2.25.1 > >