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Message-ID: <CAJaqyWejgnBngjrnuzefTVAhdjRcDOzAJfe5b0aE65uxON=G5w@mail.gmail.com>
Date: Wed, 3 Sep 2025 08:28:38 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Cindy Lu <lulu@...hat.com>,
Stefano Garzarella <sgarzare@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Laurent Vivier <lvivier@...hat.com>, virtualization@...ts.linux.dev,
linux-kernel@...r.kernel.org, Yongji Xie <xieyongji@...edance.com>,
Maxime Coquelin <mcoqueli@...hat.com>
Subject: Re: [PATCH 2/6] vduse: add vq group support
On Wed, Sep 3, 2025 at 5:58 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Mon, Sep 1, 2025 at 4:40 PM Eugenio Perez Martin <eperezma@...hat.com> wrote:
> >
> > On Mon, Sep 1, 2025 at 3:59 AM Jason Wang <jasowang@...hat.com> wrote:
> > >
> > > On Tue, Aug 26, 2025 at 7:27 PM Eugenio Pérez <eperezma@...hat.com> wrote:
> > > >
> > > > This allows sepparate 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.
> > > >
> > > > Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> > > > ---
> > > > 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 | 51 ++++++++++++++++++++++++++++--
> > > > include/uapi/linux/vduse.h | 21 +++++++++++-
> > > > 2 files changed, 68 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > index e7bced0b5542..0f4e36dd167e 100644
> > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > @@ -58,6 +58,7 @@ struct vduse_virtqueue {
> > > > struct vdpa_vq_state state;
> > > > bool ready;
> > > > bool kicked;
> > > > + u32 vq_group;
> > > > spinlock_t kick_lock;
> > > > spinlock_t irq_lock;
> > > > struct eventfd_ctx *kickfd;
> > > > @@ -114,6 +115,7 @@ struct vduse_dev {
> > > > u8 status;
> > > > u32 vq_num;
> > > > u32 vq_align;
> > > > + u32 ngroups;
> > > > struct vduse_umem *umem;
> > > > struct mutex mem_lock;
> > > > unsigned int bounce_size;
> > > > @@ -592,6 +594,13 @@ static int vduse_vdpa_set_vq_state(struct vdpa_device *vdpa, u16 idx,
> > > > return 0;
> > > > }
> > > >
> > > > +static u32 vduse_get_vq_group(struct vdpa_device *vdpa, u16 idx)
> > > > +{
> > > > + struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > > > +
> > > > + return dev->vqs[idx]->vq_group;
> > > > +}
> > > > +
> > > > static int vduse_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 idx,
> > > > struct vdpa_vq_state *state)
> > > > {
> > > > @@ -678,6 +687,28 @@ static u8 vduse_vdpa_get_status(struct vdpa_device *vdpa)
> > > > return dev->status;
> > > > }
> > > >
> > > > +static int vduse_fill_vq_groups(struct vduse_dev *dev)
> > > > +{
> > > > + /* All vqs and descs must be in vq group 0 if ngroups < 2 */
> > > > + if (dev->ngroups < 2)
> > > > + return 0;
> > > > +
> > > > + for (int i = 0; i < dev->vdev->vdpa.nvqs; ++i) {
> > > > + struct vduse_dev_msg msg = { 0 };
> > > > + int ret;
> > > > +
> > > > + msg.req.type = VDUSE_GET_VQ_GROUP;
> > > > + msg.req.vq_group.index = i;
> > > > + ret = vduse_dev_msg_sync(dev, &msg);
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + dev->vqs[i]->vq_group = msg.resp.vq_group.group;
> > > > + }
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > static void vduse_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
> > > > {
> > > > struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > > > @@ -685,6 +716,11 @@ static void vduse_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
> > > > if (vduse_dev_set_status(dev, status))
> > > > return;
> > > >
> > > > + if (((dev->status ^ status) & VIRTIO_CONFIG_S_FEATURES_OK) &&
> > > > + (status & VIRTIO_CONFIG_S_FEATURES_OK))
> > > > + if (vduse_fill_vq_groups(dev))
> > > > + return;
> > >
> > > I may lose some context but I think we've agreed that we need to
> > > extend the status response for this instead of having multiple
> > > indepdent response.
> > >
> >
> > My understanding was it is ok to start with this version by [1]. We
> > can even make it asynchronous on top if we find this is a bottleneck
> > and the VDUSE device would need no change, would that work?
>
> I think I need to understand why we can not defer this to get_group_asid() call.
>
Because we need to know the vq_groups->asid mapping in other calls
like set_group_asid or get_vq_group.
We could add a boolean on each virtqueue to track if we know its
virtqueue group and then only ask VDUSE device it if needed, would
that work?
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