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

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Message-ID: <CAJaqyWepbQBJZmDv8QuaE309EHW_GEzFUHTTKtbLM29JUXmKpw@mail.gmail.com>
Date: Thu, 18 Dec 2025 11:06:41 +0100
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Jason Wang <jasowang@...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 Thu, Dec 18, 2025 at 7:47 AM Jason Wang <jasowang@...hat.com> wrote:
>
> 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".

Sure, I'll change it in the next version.