linux-kernel - Re: [PATCH v10 2/8] vduse: add vq group support

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Message-ID: <CACGkMEuCgvKEfFCGLp1XSaa+tKM0KYvzYmpC+57ZnUuomNwV5g@mail.gmail.com>
Date: Thu, 18 Dec 2025 14:46:41 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Pérez <eperezma@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Maxime Coquelin <mcoqueli@...hat.com>, 
	Laurent Vivier <lvivier@...hat.com>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Stefano Garzarella <sgarzare@...hat.com>, 
	Yongji Xie <xieyongji@...edance.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Cindy Lu <lulu@...hat.com>
Subject: Re: [PATCH v10 2/8] vduse: add vq group support

On Wed, Dec 17, 2025 at 7:24 PM Eugenio Pérez <eperezma@...hat.com> wrote:
>
> This allows separate the different virtqueues in groups that shares the
> same address space.  Asking the VDUSE device for the groups of the vq at
> the beginning as they're needed for the DMA API.
>
> Allocating 3 vq groups as net is the device that need the most groups:
> * Dataplane (guest passthrough)
> * CVQ
> * Shadowed vrings.
>
> Future versions of the series can include dynamic allocation of the
> groups array so VDUSE can declare more groups.
>
> Acked-by: Jason Wang <jasowang@...hat.com>
> Reviewed-by: Xie Yongji <xieyongji@...edance.com>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> ---
> v6:
> * s/sepparate/separate (MST).
> * s/dev->api_version < 1/dev->api_version < VDUSE_API_VERSION_1
>
> v5:
> * Revert core vdpa changes (Jason).
> * Fix group == ngroup case in checking VQ_SETUP argument (Jason).
>
> v4:
> * Revert the "invalid vq group" concept and assume 0 if not set (Jason).
> * Make config->ngroups == 0 invalid (Jason).
>
> v3:
> * Make the default group an invalid group as long as VDUSE device does
>   not set it to some valid u32 value.  Modify the vdpa core to take that
>   into account (Jason).
> * Create the VDUSE_DEV_MAX_GROUPS instead of using a magic number
>
> v2:
> * Now the vq group is in vduse_vq_config struct instead of issuing one
>   VDUSE message per vq.
>
> v1:
> * Fix: Remove BIT_ULL(VIRTIO_S_*), as _S_ is already the bit (Maxime)
>
> RFC v3:
> * Increase VDUSE_MAX_VQ_GROUPS to 0xffff (Jason).  It was set to a lower
>   value to reduce memory consumption, but vqs are already limited to
>   that value and userspace VDUSE is able to allocate that many vqs.
> * Remove the descs vq group capability as it will not be used and we can
>   add it on top.
> * Do not ask for vq groups in number of vq groups < 2.
> * Move the valid vq groups range check to vduse_validate_config.
>
> RFC v2:
> * Cache group information in kernel, as we need to provide the vq map
>   tokens properly.
> * Add descs vq group to optimize SVQ forwarding and support indirect
>   descriptors out of the box.
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 48 ++++++++++++++++++++++++++----
>  include/uapi/linux/vduse.h         | 12 ++++++--
>  2 files changed, 52 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index ae357d014564..b012dc3557b9 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -39,6 +39,7 @@
>  #define DRV_LICENSE  "GPL v2"
>
>  #define VDUSE_DEV_MAX (1U << MINORBITS)
> +#define VDUSE_DEV_MAX_GROUPS 0xffff
>  #define VDUSE_MAX_BOUNCE_SIZE (1024 * 1024 * 1024)
>  #define VDUSE_MIN_BOUNCE_SIZE (1024 * 1024)
>  #define VDUSE_BOUNCE_SIZE (64 * 1024 * 1024)
> @@ -58,6 +59,7 @@ struct vduse_virtqueue {
>         struct vdpa_vq_state state;
>         bool ready;
>         bool kicked;
> +       u32 vq_group;

Nit, since we are under the context of virtqueue, I'd rename this as a
simple "group".

Thanks