Re: [PATCH vhost v3 00/19] virtio: drivers maintain dma info for premapped vq

Michael S. Tsirkin
2024-02-29T08:21:29Z

On Thu, Feb 29, 2024 at 03:20:25PM +0800, Xuan Zhuo wrote:
> As discussed:
> http://lore.kernel.org/all/CACGkMEvq0No8QGC46U4mGsMtuD44fD_cfLcPaVmJ3rHYqRZxYg@mail.gmail.com
>
> If the virtio is premapped mode, the driver should manage the dma info by self.
> So the virtio core should not store the dma info.
> So we can release the memory used to store the dma info.
>
> But if the desc_extra has not dma info, we face a new question,
> it is hard to get the dma info of the desc with indirect flag.
> For split mode, that is easy from desc, but for the packed mode,
> it is hard to get the dma info from the desc. And for hardening
> the dma unmap is saft, we should store the dma info of indirect
> descs.
>
> So I introduce the "structure the indirect desc table" to
> allocate space to store dma info with the desc table.
>
> On the other side, we mix the descs with indirect flag
> with other descs together to share the unmap api. That
> is complex. I found if we we distinguish the descs with
> VRING_DESC_F_INDIRECT before unmap, thing will be clearer.
>
> Because of the dma array is allocated in the find_vqs(),
> so I introduce a new parameter to find_vqs().
>
> Note:
> this is on the top of
> [PATCH vhost v1] virtio: packed: fix unmap leak for indirect desc table
> http://lore.kernel.org/all/20240223071833.26095-1-xuanzhuo@linux.alibaba.com
>
> Please review.
>
> Thanks
>
> v3:
> 1. fix the conflict with the vp_modern_create_avq().

Okay but are you going to address huge memory waste all this is causing for
- people who never do zero copy
- systems where dma unmap is a nop

?

You should address all comments when you post a new version, not just
what was expedient, or alternatively tag patch as RFC and explain
in commit log that you plan to do it later.

> v2:
> 1. change the dma item of virtio-net, every item have MAX_SKB_FRAGS + 2
> addr + len pairs.
> 2. introduce virtnet_sq_free_stats for __free_old_xmit
>
> v1:
> 1. rename transport_vq_config to vq_transport_config
> 2. virtio-net set dma meta number to (ring-size + 1)(MAX_SKB_FRGAS +2)
> 3. introduce virtqueue_dma_map_sg_attrs
> 4. separate vring_create_virtqueue to an independent commit
>
>
>
> Xuan Zhuo (19):
> virtio_ring: introduce vring_need_unmap_buffer
> virtio_ring: packed: remove double check of the unmap ops
> virtio_ring: packed: structure the indirect desc table
> virtio_ring: split: remove double check of the unmap ops
> virtio_ring: split: structure the indirect desc table
> virtio_ring: no store dma info when unmap is not needed
> virtio: find_vqs: pass struct instead of multi parameters
> virtio: vring_create_virtqueue: pass struct instead of multi
> parameters
> virtio: vring_new_virtqueue(): pass struct instead of multi parameters
> virtio_ring: simplify the parameters of the funcs related to
> vring_create/new_virtqueue()
> virtio: find_vqs: add new parameter premapped
> virtio_ring: export premapped to driver by struct virtqueue
> virtio_net: set premapped mode by find_vqs()
> virtio_ring: remove api of setting vq premapped
> virtio_ring: introduce dma map api for page
> virtio_ring: introduce virtqueue_dma_map_sg_attrs
> virtio_net: unify the code for recycling the xmit ptr
> virtio_net: rename free_old_xmit_skbs to free_old_xmit
> virtio_net: sq support premapped mode
>
> arch/um/drivers/virtio_uml.c | 31 +-
> drivers/net/virtio_net.c | 283 ++++++---
> drivers/platform/mellanox/mlxbf-tmfifo.c | 24 +-
> drivers/remoteproc/remoteproc_virtio.c | 31 +-
> drivers/s390/virtio/virtio_ccw.c | 33 +-
> drivers/virtio/virtio_mmio.c | 30 +-
> drivers/virtio/virtio_pci_common.c | 59 +-
> drivers/virtio/virtio_pci_common.h | 9 +-
> drivers/virtio/virtio_pci_legacy.c | 16 +-
> drivers/virtio/virtio_pci_modern.c | 38 +-
> drivers/virtio/virtio_ring.c | 698 ++++++++++++-----------
> drivers/virtio/virtio_vdpa.c | 45 +-
> include/linux/virtio.h | 13 +-
> include/linux/virtio_config.h | 48 +-
> include/linux/virtio_ring.h | 82 +--
> tools/virtio/virtio_test.c | 4 +-
> tools/virtio/vringh_test.c | 28 +-
> 17 files changed, 847 insertions(+), 625 deletions(-)
>
> --
> 2.32.0.3.g01195cf9f