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Message-ID: <CAJaqyWeHLw9CUEkH1KF8np2zJMC-zMRU6AFRJEhczzuF7MNU8A@mail.gmail.com>
Date: Mon, 1 Sep 2025 10:39:31 +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 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?
> > +
> > dev->status = status;
> > }
> >
> > @@ -789,6 +825,7 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
> > .set_vq_cb = vduse_vdpa_set_vq_cb,
> > .set_vq_num = vduse_vdpa_set_vq_num,
> > .get_vq_size = vduse_vdpa_get_vq_size,
> > + .get_vq_group = vduse_get_vq_group,
> > .set_vq_ready = vduse_vdpa_set_vq_ready,
> > .get_vq_ready = vduse_vdpa_get_vq_ready,
> > .set_vq_state = vduse_vdpa_set_vq_state,
> > @@ -1737,12 +1774,19 @@ static bool features_is_valid(struct vduse_dev_config *config)
> > return true;
> > }
> >
> > -static bool vduse_validate_config(struct vduse_dev_config *config)
> > +static bool vduse_validate_config(struct vduse_dev_config *config,
> > + u64 api_version)
> > {
> > if (!is_mem_zero((const char *)config->reserved,
> > sizeof(config->reserved)))
> > return false;
> >
> > + if (api_version < VDUSE_API_VERSION_1 && config->ngroups)
> > + return false;
> > +
> > + if (api_version >= VDUSE_API_VERSION_1 && config->ngroups > 0xffff)
> > + return false;
>
> Let's use a macro instead of magic number.
>
The rest of the limits are hardcoded, but I'm ok with changing this.
Is UINT16_MAX ok here, or do you prefer something like MAX_NGROUPS and
MAX_ASID?
[...]
[1] https://patchew.org/linux/20250807115752.1663383-1-eperezma@redhat.com/20250807115752.1663383-3-eperezma@redhat.com/#CACGkMEuVngGjgPZXnajiPC+pcbt+dr6jqKRQr8OcX7HK1W3WNQ@mail.gmail.com
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