linux-kernel - Re: [PATCH 0/9] Refine virtio mapping API

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Message-ID: <20250701030150-mutt-send-email-mst@kernel.org>
Date: Tue, 1 Jul 2025 03:04:14 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
	hch@...radead.org, xieyongji@...edance.com
Subject: Re: [PATCH 0/9] Refine virtio mapping API

On Tue, Jul 01, 2025 at 09:13:52AM +0800, Jason Wang wrote:
> Hi all:
> 
> Virtio used to be coupled with DMA API. This works fine for the device
> that do real DMA but not the others. For example, VDUSE nees to craft
> with DMA API in order to let the virtio-vdpa driver to work.
> 
> This series tries to solve this issue by introducing the mapping API
> in the virtio core. So transport like vDPA can implement their own
> mapping logic without the need to hack with DMA API. The mapping API
> are abstracted with a new map operations in order to be re-used by
> transprot or device. So device like VDUSE can implement its own
> mapping loigc.
> 
> Please review.
> 
> Thanks

Cost of all this extra indirection? Especially on systems with
software spectre mitigations/retpoline enabled.

> Jason Wang (9):
>   virtio_ring: constify virtqueue pointer for DMA helpers
>   virtio_ring: switch to use dma_{map|unmap}_page()
>   virtio: rename dma helpers
>   virtio: rename dma_dev to map_token
>   virtio_ring: rename dma_handle to map_handle
>   virtio: introduce map ops in virtio core
>   vdpa: rename dma_dev to map_token
>   vdpa: introduce map ops
>   vduse: switch to use virtio map API instead of DMA API
> 
>  drivers/net/virtio_net.c                 |  32 +-
>  drivers/vdpa/alibaba/eni_vdpa.c          |   5 +-
>  drivers/vdpa/ifcvf/ifcvf_main.c          |   5 +-
>  drivers/vdpa/octeon_ep/octep_vdpa_main.c |   6 +-
>  drivers/vdpa/pds/vdpa_dev.c              |   3 +-
>  drivers/vdpa/solidrun/snet_main.c        |   4 +-
>  drivers/vdpa/vdpa.c                      |   5 +-
>  drivers/vdpa/vdpa_sim/vdpa_sim.c         |   4 +-
>  drivers/vdpa/vdpa_user/iova_domain.c     |   8 +-
>  drivers/vdpa/vdpa_user/iova_domain.h     |   5 +-
>  drivers/vdpa/vdpa_user/vduse_dev.c       |  34 +-
>  drivers/vdpa/virtio_pci/vp_vdpa.c        |   5 +-
>  drivers/vhost/vdpa.c                     |  11 +-
>  drivers/virtio/virtio_ring.c             | 440 ++++++++++++++---------
>  drivers/virtio/virtio_vdpa.c             |  15 +-
>  include/linux/vdpa.h                     |  22 +-
>  include/linux/virtio.h                   |  36 +-
>  include/linux/virtio_config.h            |  68 ++++
>  include/linux/virtio_ring.h              |   6 +-
>  19 files changed, 476 insertions(+), 238 deletions(-)
> 
> -- 
> 2.34.1