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Message-ID: <CACGkMEuZq2NaS9icynhrgZtXQ26fDFFpFrP3bUwDXLCR6uN4qw@mail.gmail.com>
Date: Tue, 12 Aug 2025 11:01:23 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Perez Martin <eperezma@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Cindy Lu <lulu@...hat.com>,
Yongji Xie <xieyongji@...edance.com>, Stefano Garzarella <sgarzare@...hat.com>,
virtualization@...ts.linux.dev, Laurent Vivier <lvivier@...hat.com>,
linux-kernel@...r.kernel.org, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Maxime Coquelin <mcoqueli@...hat.com>
Subject: Re: [RFC v2 2/7] vduse: add vq group support
On Mon, Aug 11, 2025 at 5:52 PM Eugenio Perez Martin
<eperezma@...hat.com> wrote:
>
> On Mon, Aug 11, 2025 at 5:10 AM Jason Wang <jasowang@...hat.com> wrote:
> >
> > On Thu, Aug 7, 2025 at 7:58 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>
> > > ---
> > > 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 | 71 +++++++++++++++++++++++++++++-
> > > include/uapi/linux/vduse.h | 19 +++++++-
> > > 2 files changed, 88 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > index d858c4389cc1..d1f6d00a9c71 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -46,6 +46,11 @@
> > > #define VDUSE_IOVA_SIZE (VDUSE_MAX_BOUNCE_SIZE + 128 * 1024 * 1024)
> > > #define VDUSE_MSG_DEFAULT_TIMEOUT 30
> > >
> > > +/*
> > > + * Let's make it 3 for simplicity.
> > > + */
> > > +#define VDUSE_MAX_VQ_GROUPS 3
> >
> > I think we can release this to something like 64. Otherwise we might
> > bump the version again just to increase the limitation? Or having a
> > sysfs entry like bounce_size?
> >
>
> I think it should not be linked to the version, but it is true there
> is no way for VDUSE devices to check the maximum VQ groups / ASID that
> the kernel supports.
>
> To handle as bounce_size seems the best option, good point. I'll send
> a new version with that!
>
> > > +
> > > #define IRQ_UNBOUND -1
> > >
> > > struct vduse_virtqueue {
> > > @@ -58,6 +63,8 @@ struct vduse_virtqueue {
> > > struct vdpa_vq_state state;
> > > bool ready;
> > > bool kicked;
> > > + u32 vq_group;
> > > + u32 vq_desc_group;
> > > spinlock_t kick_lock;
> > > spinlock_t irq_lock;
> > > struct eventfd_ctx *kickfd;
> > > @@ -114,6 +121,7 @@ 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 +600,20 @@ 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 u32 vduse_get_vq_desc_group(struct vdpa_device *vdpa, u16 idx)
> > > +{
> > > + struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > > +
> > > + return dev->vqs[idx]->vq_desc_group;
> > > +}
> > > +
> > > static int vduse_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 idx,
> > > struct vdpa_vq_state *state)
> > > {
> > > @@ -678,13 +700,48 @@ static u8 vduse_vdpa_get_status(struct vdpa_device *vdpa)
> > > return dev->status;
> > > }
> > >
> > > +static int vduse_fill_vq_groups(struct vduse_dev *dev)
> > > +{
> > > + if (dev->api_version < VDUSE_API_VERSION_1)
> > > + 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);
> >
> > I fail to understand why the default group mapping is not done during
> > device creation.
> >
>
> Because it changes depending on the features.
>
> If a new device has 5 virtqueues and the device wants to isolate the
> CVQ, the CVQ position depends on the features that the guest's acks:
> * If MQ is acked the isolated vq is #5
> * If MQ is not acked the isolated vq is #3.
I see we are still damaged by the design of the cvq index. But this is
just a static branch not a dynamic one. If we can find ways to make it
static it would be better.
>
> > > + if (ret)
> > > + return ret;
> > > +
> > > + dev->vqs[i]->vq_group = msg.resp.vq_group.num;
> > > +
> > > + msg.req.type = VDUSE_GET_VRING_DESC_GROUP;
> > > + ret = vduse_dev_msg_sync(dev, &msg);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + dev->vqs[i]->vq_desc_group = msg.resp.vq_group.num;
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > static void vduse_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
> > > {
> > > struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > > + u8 previous_status = dev->status;
> > >
> > > if (vduse_dev_set_status(dev, status))
> > > return;
> > >
> > > + if ((dev->status ^ previous_status) &
> > > + BIT_ULL(VIRTIO_CONFIG_S_FEATURES_OK) &&
> > > + status & (1ULL << VIRTIO_CONFIG_S_FEATURES_OK))
> > > + if (vduse_fill_vq_groups(dev))
> >
> > Can we merge the two messages into a single one? Or can we use a
> > shared memory for storing such mapping?
> >
> > For example, if we have 256 queues it would be very slow.
> >
>
> To merge it in the same message is good to me, sure.
We can start from this if we can't find a way to provision vq to group
mapping during device creation.
> To make it a
> table in shm seems more complicated, unless we accept a void * in the
> reply and VDUSE uses copy_from_user. If that is ok here, then sure.
>
This looks tricky indeed.
Thanks
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