On Tue, Apr 24, 2018 at 04:43:22AM +0300, Michael S. Tsirkin wrote: > On Tue, Apr 24, 2018 at 09:37:47AM +0800, Tiwei Bie wrote: > > On Tue, Apr 24, 2018 at 04:29:51AM +0300, Michael S. Tsirkin wrote: > > > On Tue, Apr 24, 2018 at 09:16:38AM +0800, Tiwei Bie wrote: > > > > On Tue, Apr 24, 2018 at 04:05:07AM +0300, Michael S. Tsirkin wrote: > > > > > On Tue, Apr 24, 2018 at 08:54:52AM +0800, Jason Wang wrote: > > > > > > > > > > > > > > > > > > On 2018年04月23日 17:29, Tiwei Bie wrote: > > > > > > > On Mon, Apr 23, 2018 at 01:42:14PM +0800, Jason Wang wrote: > > > > > > > > On 2018年04月01日 22:12, Tiwei Bie wrote: > > > > > > > > > Hello everyone, > > > > > > > > > > > > > > > > > > This RFC implements packed ring support for virtio driver. > > > > > > > > > > > > > > > > > > The code was tested with DPDK vhost (testpmd/vhost-PMD) implemented > > > > > > > > > by Jens at http://dpdk.org/ml/archives/dev/2018-January/089417.html > > > > > > > > > Minor changes are needed for the vhost code, e.g. to kick the guest. > > > > > > > > > > > > > > > > > > TODO: > > > > > > > > > - Refinements and bug fixes; > > > > > > > > > - Split into small patches; > > > > > > > > > - Test indirect descriptor support; > > > > > > > > > - Test/fix event suppression support; > > > > > > > > > - Test devices other than net; > > > > > > > > > > > > > > > > > > RFC v1 -> RFC v2: > > > > > > > > > - Add indirect descriptor support - compile test only; > > > > > > > > > - Add event suppression supprt - compile test only; > > > > > > > > > - Move vring_packed_init() out of uapi (Jason, MST); > > > > > > > > > - Merge two loops into one in virtqueue_add_packed() (Jason); > > > > > > > > > - Split vring_unmap_one() for packed ring and split ring (Jason); > > > > > > > > > - Avoid using '%' operator (Jason); > > > > > > > > > - Rename free_head -> next_avail_idx (Jason); > > > > > > > > > - Add comments for virtio_wmb() in virtqueue_add_packed() (Jason); > > > > > > > > > - Some other refinements and bug fixes; > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > > > > > > > > > Signed-off-by: Tiwei Bie <tiwei.bie@xxxxxxxxx> > > > > > > > > > --- > > > > > > > > > drivers/virtio/virtio_ring.c | 1094 +++++++++++++++++++++++++++++------- > > > > > > > > > include/linux/virtio_ring.h | 8 +- > > > > > > > > > include/uapi/linux/virtio_config.h | 12 +- > > > > > > > > > include/uapi/linux/virtio_ring.h | 61 ++ > > > > > > > > > 4 files changed, 980 insertions(+), 195 deletions(-) > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > > > > > > > index 71458f493cf8..0515dca34d77 100644 > > > > > > > > > --- a/drivers/virtio/virtio_ring.c > > > > > > > > > +++ b/drivers/virtio/virtio_ring.c > > > > > > > > > @@ -58,14 +58,15 @@ > > > > > > > > [...] > > > > > > > > > > > > > > > > > + > > > > > > > > > + if (vq->indirect) { > > > > > > > > > + u32 len; > > > > > > > > > + > > > > > > > > > + desc = vq->desc_state[head].indir_desc; > > > > > > > > > + /* Free the indirect table, if any, now that it's unmapped. */ > > > > > > > > > + if (!desc) > > > > > > > > > + goto out; > > > > > > > > > + > > > > > > > > > + len = virtio32_to_cpu(vq->vq.vdev, > > > > > > > > > + vq->vring_packed.desc[head].len); > > > > > > > > > + > > > > > > > > > + BUG_ON(!(vq->vring_packed.desc[head].flags & > > > > > > > > > + cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT))); > > > > > > > > It looks to me spec does not force to keep VRING_DESC_F_INDIRECT here. So we > > > > > > > > can safely remove this BUG_ON() here. > > > > > > > > > > > > > > > > > + BUG_ON(len == 0 || len % sizeof(struct vring_packed_desc)); > > > > > > > > Len could be ignored for used descriptor according to the spec, so we need > > > > > > > > remove this BUG_ON() too. > > > > > > > Yeah, you're right! The BUG_ON() isn't right. I'll remove it. > > > > > > > And I think something related to this in the spec isn't very > > > > > > > clear currently. > > > > > > > > > > > > > > In the spec, there are below words: > > > > > > > > > > > > > > https://github.com/oasis-tcs/virtio-spec/blob/d4fec517dfcf/packed-ring.tex#L272 > > > > > > > """ > > > > > > > In descriptors with VIRTQ_DESC_F_INDIRECT set VIRTQ_DESC_F_WRITE > > > > > > > is reserved and is ignored by the device. > > > > > > > """ > > > > > > > > > > > > > > So when device writes back an used descriptor in this case, > > > > > > > device may not set the VIRTQ_DESC_F_WRITE flag as the flag > > > > > > > is reserved and should be ignored. > > > > > > > > > > > > > > https://github.com/oasis-tcs/virtio-spec/blob/d4fec517dfcf/packed-ring.tex#L170 > > > > > > > """ > > > > > > > Element Length is reserved for used descriptors without the > > > > > > > VIRTQ_DESC_F_WRITE flag, and is ignored by drivers. > > > > > > > """ > > > > > > > > > > > > > > And this is the way how driver ignores the `len` in an used > > > > > > > descriptor. > > > > > > > > > > > > > > https://github.com/oasis-tcs/virtio-spec/blob/d4fec517dfcf/packed-ring.tex#L241 > > > > > > > """ > > > > > > > To increase ring capacity the driver can store a (read-only > > > > > > > by the device) table of indirect descriptors anywhere in memory, > > > > > > > and insert a descriptor in the main virtqueue (with \field{Flags} > > > > > > > bit VIRTQ_DESC_F_INDIRECT on) that refers to a buffer element > > > > > > > containing this indirect descriptor table; > > > > > > > """ > > > > > > > > > > > > > > So the indirect descriptors in the table are read-only by > > > > > > > the device. And the only descriptor which is writeable by > > > > > > > the device is the descriptor in the main virtqueue (with > > > > > > > Flags bit VIRTQ_DESC_F_INDIRECT on). So if we ignore the > > > > > > > `len` in this descriptor, we won't be able to get the > > > > > > > length of the data written by the device. > > > > > > > > > > > > > > So I think the `len` in this descriptor will carry the > > > > > > > length of the data written by the device (if the buffers > > > > > > > are writable to the device) even if the VIRTQ_DESC_F_WRITE > > > > > > > isn't set by the device. How do you think? > > > > > > > > > > > > Yes I think so. But we'd better need clarification from Michael. > > > > > > > > > > I think if you use a descriptor, and you want to supply len > > > > > to guest, you set VIRTQ_DESC_F_WRITE in the used descriptor. > > > > > Spec also says you must not set VIRTQ_DESC_F_INDIRECT then. > > > > > If that's a problem we could look at relaxing that last requirement - > > > > > does driver want INDIRECT in used descriptor to match > > > > > the value in the avail descriptor for some reason? > > > > > > > > For indirect, driver needs some way to get the length > > > > of the data written by the driver. And the descriptors > > > > in the indirect table is read-only, so the only place > > > > device could put this value is the descriptor with the > > > > VIRTQ_DESC_F_INDIRECT flag set. > > > > > > when writing out used descriptor, device should set VIRTQ_DESC_F_WRITE > > > (and clear VIRTQ_DESC_F_INDIRECT). > > > > So the spec allows device to set VIRTQ_DESC_F_WRITE bit > > when writing out an used descriptor even if the corresponding > > descriptors it just parsed don't have the VIRTQ_DESC_F_WRITE > > bit set? > > > > Best regards, > > Tiwei Bie > > I think so. In a used descriptor, VIRTQ_DESC_F_WRITE just means length > is valid. Got it. It's very neat. Thanks! :) Best regards, Tiwei Bie > > -- > MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
