----- Original Message ----- > From: "Xuan Zhuo" <xuanzhuo@xxxxxxxxxxxxxxxxx> > To: "Guo Zhi" <qtxuning1999@xxxxxxxxxxx> > Cc: "netdev" <netdev@xxxxxxxxxxxxxxx>, "linux-kernel" <linux-kernel@xxxxxxxxxxxxxxx>, "kvm list" <kvm@xxxxxxxxxxxxxxx>, > "virtualization" <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, "Guo Zhi" <qtxuning1999@xxxxxxxxxxx>, "eperezma" > <eperezma@xxxxxxxxxx>, "jasowang" <jasowang@xxxxxxxxxx>, "sgarzare" <sgarzare@xxxxxxxxxx>, "Michael Tsirkin" > <mst@xxxxxxxxxx> > Sent: Thursday, August 18, 2022 11:05:37 AM > Subject: Re: [RFC v2 5/7] virtio: unmask F_NEXT flag in desc_extra > On Wed, 17 Aug 2022 21:57:16 +0800, Guo Zhi <qtxuning1999@xxxxxxxxxxx> wrote: >> We didn't unmask F_NEXT flag in desc_extra in the end of a chain, >> unmask it so that we can access desc_extra to get next information. > > I think we should state the purpose of this. > I have to unmask F_NEXT flag in desc_extra in this series, because if in order negotiated, the driver has to iterate the descriptor chain to get chain length from desc_extra. (The reason why we should use desc_extra is that descs may be changed by malicious hypervisors, https://lkml.org/lkml/2022/7/26/224). >> >> Signed-off-by: Guo Zhi <qtxuning1999@xxxxxxxxxxx> >> --- >> drivers/virtio/virtio_ring.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c >> index a5ec724c01d8..1c1b3fa376a2 100644 >> --- a/drivers/virtio/virtio_ring.c >> +++ b/drivers/virtio/virtio_ring.c >> @@ -567,7 +567,7 @@ 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; >> >> @@ -584,6 +584,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, >> total_sg * sizeof(struct vring_desc), >> VRING_DESC_F_INDIRECT, >> false); >> + vq->split.desc_extra[head & (vq->split.vring.num - 1)].flags &= >> + ~VRING_DESC_F_NEXT; > > This seems unnecessary. > >> } >> >> /* We're using some buffers from the free list. */ >> @@ -693,7 +695,7 @@ 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) { > > nextflag is __virtio16 > > You can use VRING_DESC_F_NEXT directly. > > Thanks. Sorry for the mistake, I will fix it. > >> vring_unmap_one_split(vq, i); >> i = vq->split.desc_extra[i].next; >> vq->vq.num_free++; >> -- >> 2.17.1 >>
