Re: [PATCH v3 3/3] vduse: add F_QUEUE_READY feature

From: Eugenio Perez Martin

Date: Fri Mar 27 2026 - 02:46:02 EST

On Fri, Mar 27, 2026 at 2:15 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
> On Thu, Mar 26, 2026 at 2:57 PM Eugenio Perez Martin
> <eperezma@xxxxxxxxxx> wrote:
> >
> > On Thu, Mar 26, 2026 at 3:44 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > >
> > > On Tue, Mar 24, 2026 at 11:24 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> > > >
> > > > On Tue, Mar 24, 2026 at 03:01:47PM +0100, Eugenio Perez Martin wrote:
> > > > > On Fri, Mar 13, 2026 at 8:08 AM Eugenio Perez Martin
> > > > > <eperezma@xxxxxxxxxx> wrote:
> > > > > >
> > > > > > On Fri, Mar 13, 2026 at 7:05 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Thu, Mar 12, 2026 at 2:24 PM Eugenio Perez Martin
> > > > > > > <eperezma@xxxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > > On Thu, Mar 12, 2026 at 4:58 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > > > > > > > >
> > > > > > > > > On Wed, Mar 11, 2026 at 3:08 AM Eugenio Pérez <eperezma@xxxxxxxxxx> wrote:
> > > > > > > > > >
> > > > > > > > > > Add the VDUSE_F_QUEUE_READY feature flag. This allows the kernel module
> > > > > > > > > > to explicitly signal userspace when a specific virtqueue has been
> > > > > > > > > > enabled.
> > > > > > > > > >
> > > > > > > > > > In scenarios like Live Migration of VirtIO net devices, the dataplane
> > > > > > > > > > starts after the control virtqueue allowing QEMU to apply configuration
> > > > > > > > > > in the destination device.
> > > > > > > > > >
> > > > > > > > > > Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> > > > > > > > > > ---
> > > > > > > > > > v2:
> > > > > > > > > > * Fix comment of vduse_dev_request.vq_ready
> > > > > > > > > > * Set vq_ready before sending the message to the VDUSE userland
> > > > > > > > > > instance, avoiding the need for SMP sync after receiving the message.
> > > > > > > > > > ---
> > > > > > > > > > drivers/vdpa/vdpa_user/vduse_dev.c | 28 +++++++++++++++++++++++++++-
> > > > > > > > > > include/uapi/linux/vduse.h | 18 ++++++++++++++++++
> > > > > > > > > > 2 files changed, 45 insertions(+), 1 deletion(-)
> > > > > > > > > >
> > > > > > > > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > > > > index 17e0358d3a68..4f642b95a7cb 100644
> > > > > > > > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > > > > @@ -9,6 +9,7 @@
> > > > > > > > > > */
> > > > > > > > > >
> > > > > > > > > > #include "linux/virtio_net.h"
> > > > > > > > > > +#include <linux/bits.h>
> > > > > > > > > > #include <linux/cleanup.h>
> > > > > > > > > > #include <linux/init.h>
> > > > > > > > > > #include <linux/module.h>
> > > > > > > > > > @@ -53,7 +54,7 @@
> > > > > > > > > > #define IRQ_UNBOUND -1
> > > > > > > > > >
> > > > > > > > > > /* Supported VDUSE features */
> > > > > > > > > > -static const uint64_t vduse_features;
> > > > > > > > > > +static const uint64_t vduse_features = BIT_U64(VDUSE_F_QUEUE_READY);
> > > > > > > > > >
> > > > > > > > > > /*
> > > > > > > > > > * VDUSE instance have not asked the vduse API version, so assume 0.
> > > > > > > > > > @@ -120,6 +121,7 @@ struct vduse_dev {
> > > > > > > > > > char *name;
> > > > > > > > > > struct mutex lock;
> > > > > > > > > > spinlock_t msg_lock;
> > > > > > > > > > + u64 vduse_features;
> > > > > > > > > > u64 msg_unique;
> > > > > > > > > > u32 msg_timeout;
> > > > > > > > > > wait_queue_head_t waitq;
> > > > > > > > > > @@ -601,8 +603,29 @@ static void vduse_vdpa_set_vq_ready(struct vdpa_device *vdpa,
> > > > > > > > > > {
> > > > > > > > > > struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > > > > > > > > > struct vduse_virtqueue *vq = dev->vqs[idx];
> > > > > > > > > > + struct vduse_dev_msg msg = { 0 };
> > > > > > > > > > + int r;
> > > > > > > > > >
> > > > > > > > > > vq->ready = ready;
> > > > > > > > > > +
> > > > > > > > > > + if (!(dev->vduse_features & BIT_U64(VDUSE_F_QUEUE_READY)))
> > > > > > > > > > + return;
> > > > > > > > > > +
> > > > > > > > > > + msg.req.type = VDUSE_SET_VQ_READY;
> > > > > > > > > > + msg.req.vq_ready.num = idx;
> > > > > > > > > > + msg.req.vq_ready.ready = !!ready;
> > > > > > > > > > +
> > > > > > > > > > + r = vduse_dev_msg_sync(dev, &msg);
> > > > > > > > > > +
> > > > > > > > > > + if (r < 0) {
> > > > > > > > > > + dev_dbg(&vdpa->dev, "device refuses to set vq %u ready %u",
> > > > > > > > > > + idx, ready);
> > > > > > > > > > +
> > > > > > > > > > + /* We can't do better than break the device in this case */
> > > > > > > > >
> > > > > > > > > It's better to explain why we can't depend on vduse_dev_msg_sync() here.
> > > > > > > > >
> > > > > > > > > For example it did:
> > > > > > > > >
> > > > > > > > > if (unlikely(dev->broken))
> > > > > > > > > return -EIO;
> > > > > > > > >
> > > > > > > > > init_waitqueue_head(&msg->waitq);
> > > > > > > > > spin_lock(&dev->msg_lock);
> > > > > > > > > if (unlikely(dev->broken)) {
> > > > > > > > > spin_unlock(&dev->msg_lock);
> > > > > > > > > return -EIO;
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > and
> > > > > > > > >
> > > > > > > > > if (!msg->completed) {
> > > > > > > > > list_del(&msg->list);
> > > > > > > > > msg->resp.result = VDUSE_REQ_RESULT_FAILED;
> > > > > > > > > /* Mark the device as malfunction when there is a timeout */
> > > > > > > > > if (!ret)
> > > > > > > > > vduse_dev_broken(dev);
> > > > > > > > > }
> > > > > > > > >
> > > > > > > >
> > > > > > > > I'm not sure I follow you here.
> > > > > > > >
> > > > > > > > We can't do better than breaking the device because the function
> > > > > > > > returns no error state, and the caller does not expect an error code.
> > > > > > > > Do you mean we can't depend on vduse_dev_msg_sync to call
> > > > > > > > vduse_dev_broken(dev) by itself?
> > > > > > >
> > > > > > > I think I meant, reset seems to be more heavyweight than suspend.
> > > > > > >
> > > > > > > So if reset can fail, I don't see reason ot break device only for
> > > > > > > suspend failure.
> > > > > > >
> > > > > >
> > > > > > Sorry I still don't get you.
> > > > > >
> > > > > > This series does not implement suspend at all. It doesn't modify the
> > > > > > VDUSE device reset or the virtio reset behavior. It only implements
> > > > > > the vq ready message for the device. If the device returns an error
> > > > > > from that operation, what is your proposal for when the driver sends
> > > > > > new messages like resume?
> > > > > >
> > > > >
> > > > > Friendly ping.
> > > >
> > > > Jason, more comments? If this is to go in it has to go into linux next.
> > >
> > > A typo, basically I meant that reset is more heavyweight than queue
> > > ready. If we decide to check the response for queue ready, we need to
> > > check the reset as well.
> > >
> > > But I'm fine if you think we can start from this.
> > >
> >
> > If you mean something like this:
> > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
> > b/drivers/vdpa/vdpa_user/vduse_dev.c
> > index 6202f6902fcd..23b850023417 100644
> > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > @@ -816,7 +816,8 @@ static int vduse_vdpa_reset(struct vdpa_device *vdpa)
> > struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > int ret = vduse_dev_set_status(dev, 0);
> >
> > - vduse_dev_reset(dev);
> > + if (ret == 0)
> > + vduse_dev_reset(dev);
>
> Something like this but we need to check if it's a timeout as queue ready.
>

What should VDUSE or vdpa layer do differently if it is a timeout vs
returning an error?

> >
> > return ret;
> > }
> >
> > ---
> >
> > I totally agree. But in my opinion, it's outside this series' scope. I
> > can send a patch on top.
> >
>
> Works for me.
>
> Thanks
>