On Tue, Feb 3, 2026 at 3:28 PM Eugenio Perez Martin <[email protected]> wrote:
>
> On Tue, Feb 3, 2026 at 5:00 AM Jason Wang <[email protected]> wrote:
> >
> > On Fri, Jan 30, 2026 at 4:15 PM Eugenio Perez Martin
> > <[email protected]> wrote:
> > >
> > > On Fri, Jan 30, 2026 at 3:17 AM Jason Wang <[email protected]> wrote:
> > > >
> > > > On Thu, Jan 29, 2026 at 2:26 PM Eugenio Perez Martin
> > > > <[email protected]> wrote:
> > > > >
> > > > > On Thu, Jan 29, 2026 at 3:12 AM Jason Wang <[email protected]>
> > > > > wrote:
> > > > > >
> > > > > > On Wed, Jan 28, 2026 at 8:45 PM Eugenio Pérez <[email protected]>
> > > > > > 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 <[email protected]>
> > > > > > > ---
> > > > > > > drivers/vdpa/vdpa_user/vduse_dev.c | 28
> > > > > > > +++++++++++++++++++++++++++-
> > > > > > > include/uapi/linux/vduse.h | 19 +++++++++++++++++++
> > > > > > > 2 files changed, 46 insertions(+), 1 deletion(-)
> > > > > > >
> > > > > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > index e7da69c2ad71..1d93b540db4d 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;
> > > > > > > @@ -619,7 +621,30 @@ 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;
> > > > > > > +
> > > > > > > + if (!(dev->vduse_features & BIT_U64(VDUSE_F_QUEUE_READY)))
> > > > > > > + goto out;
> > > > > > > +
> > > > > > > + 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 */
> > > > > > > + spin_lock(&dev->msg_lock);
> > > > > > > + vduse_dev_broken(dev);
> > > > > >
> > > > > > This has been done by vduse_dev_msg_sync().
> > > > > >
> > > > >
> > > > > This is done by msg_sync() when userland does not reply in a
> > > > > timeframe, but not when userland replies with VDUSE_REQ_RESULT_FAILED.
> > > > > Should I add a comment?
> > > >
> > > > If this is not specific to Q_READY, I think we need to move it to
> > > > msg_sync() as well.
> > > >
> > >
> > > It's specific to Q_READY for me, as it's the request that returns void
> > > and has no possibility to inform of an error.
> >
> > I may miss something, I mean why consider the failure of Q_READY to be
> > more serious than the failure of other commands (e.g set_status()).
> >
>
> I'm not considering the failure of Q_READY more serious than any other
> failure. I'm breaking the device here as I cannot return the error to
> the vDPA driver: This function returns void.
Yes, and set_status() return void as well.
void virtio_add_status(struct virtio_device *dev, unsigned int status)
{
might_sleep();
=> dev->config->set_status(dev, dev->config->get_status(dev) | status);
}
>
> We can make the function return a bool or int, and then make
> vhost_vdpa and virtio_vdpa react to that error. QEMU is already
> prepared for VHOST_VDPA_SET_VRING_ENABLE to return an error, as it is
> an ioctl,
But we did:
case VHOST_VDPA_SET_VRING_ENABLE:
if (copy_from_user(&s, argp, sizeof(s)))
return -EFAULT;
ops->set_vq_ready(vdpa, idx, s.num);
return 0;
So the failure come from copy_from_user()
> and hopefully the rest of the users of
> VHOST_VDPA_SET_VRING_ENABLE are also prepared.
>
> Should I change vdpa_config_ops->set_vq_ready so it can return an
> error, as a prerequisite of this series?
Or it would be better to leave the breaking of device on
REQ_RESULT_FAILED for future investigation (not blocking this series).
>
> > >
> > > The VDUSE userland instance could reply to other requests with
> > > REQ_RESULT_FAILED and the driver still has capacity to recover from
> > > the failure.
> > > If we always break the device on every request fail, we
> > > deny that possibility.
> > >
> >
> > Thanks
> >
>
Thanks
