Re: [PATCH v2] vduse: Add suspend

[Jason Wang <jasowang@redhat.com>]

On Wed, Mar 11, 2026 at 3:10 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Implement suspend operation for vduse devices, so vhost-vdpa will offer
> that backend feature and userspace can effectively suspend the device.
>
> This is a must before get virtqueue indexes (base) for live migration,
> since the device could modify them after userland gets them.

As discussed in the pervious version, let's explain why and the plan
to support resume.

>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
> This patch depends on
> https://lore.kernel.org/lkml/20260310190759.1097506-1-eperezma@redhat.com
>
> v2:
> * Take the rwsem only before the actual kick, not in vduse_vdpa_kick_vq.
>   This assures that we're not in a critical section.
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 86 +++++++++++++++++++++++++++++-
>  include/uapi/linux/vduse.h         |  4 ++
>  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 4f642b95a7cb..f56b1e3eb82d 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -54,7 +54,8 @@
>  #define IRQ_UNBOUND -1
>
>  /* Supported VDUSE features */
> -static const uint64_t vduse_features = BIT_U64(VDUSE_F_QUEUE_READY);
> +static const uint64_t vduse_features = BIT_U64(VDUSE_F_QUEUE_READY) |
> +                                      BIT_U64(VDUSE_F_SUSPEND);
>
>  /*
>   * VDUSE instance have not asked the vduse API version, so assume 0.
> @@ -85,6 +86,7 @@ struct vduse_virtqueue {
>         int irq_effective_cpu;
>         struct cpumask irq_affinity;
>         struct kobject kobj;
> +       struct vduse_dev *dev;
>  };
>
>  struct vduse_dev;
> @@ -134,6 +136,7 @@ struct vduse_dev {
>         int minor;
>         bool broken;
>         bool connected;
> +       bool suspended;
>         u64 api_version;
>         u64 device_features;
>         u64 driver_features;
> @@ -480,6 +483,7 @@ static void vduse_dev_reset(struct vduse_dev *dev)
>
>         down_write(&dev->rwsem);
>
> +       dev->suspended = false;
>         dev->status = 0;
>         dev->driver_features = 0;
>         dev->generation++;
> @@ -538,6 +542,10 @@ static void vduse_vq_kick(struct vduse_virtqueue *vq)
>         if (!vq->ready)
>                 goto unlock;
>
> +       guard(rwsem_read)(&vq->dev->rwsem);
> +       if (vq->dev->suspended)
> +               return;

Any reason for this? E.g We don't do this for other transports.

Everything else looks good.

Thanks