Re: [PATCH v6 3/4] vhost-vdpa: uAPI to suspend the device

[Eugenio Perez Martin]

On Tue, Jun 28, 2022 at 3:45 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
>
> On Thu, Jun 23, 2022 at 06:07:37PM +0200, Eugenio Pérez wrote:
> >The ioctl adds support for suspending the device from userspace.
> >
> >This is a must before getting virtqueue indexes (base) for live migration,
> >since the device could modify them after userland gets them. There are
> >individual ways to perform that action for some devices
> >(VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...) but there was no
> >way to perform it for any vhost device (and, in particular, vhost-vdpa).
> >
> >After a successful return of the ioctl call the device must not process
> >more virtqueue descriptors. The device can answer to read or writes of
> >config fields as if it were not suspended. In particular, writing to
> >"queue_enable" with a value of 1 will not make the device start
> >processing buffers of the virtqueue.
> >
> >Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> >---
> > drivers/vhost/vdpa.c       | 19 +++++++++++++++++++
> > include/uapi/linux/vhost.h | 14 ++++++++++++++
> > 2 files changed, 33 insertions(+)
> >
> >diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> >index 3d636e192061..7fa671ac4bdf 100644
> >--- a/drivers/vhost/vdpa.c
> >+++ b/drivers/vhost/vdpa.c
> >@@ -478,6 +478,22 @@ static long vhost_vdpa_get_vqs_count(struct vhost_vdpa *v, u32 __user *argp)
> >       return 0;
> > }
> >
> >+/* After a successful return of ioctl the device must not process more
> >+ * virtqueue descriptors. The device can answer to read or writes of config
> >+ * fields as if it were not suspended. In particular, writing to "queue_enable"
> >+ * with a value of 1 will not make the device start processing buffers.
> >+ */
> >+static long vhost_vdpa_suspend(struct vhost_vdpa *v)
> >+{
> >+      struct vdpa_device *vdpa = v->vdpa;
> >+      const struct vdpa_config_ops *ops = vdpa->config;
> >+
> >+      if (!ops->suspend)
> >+              return -EOPNOTSUPP;
> >+
> >+      return ops->suspend(vdpa);
> >+}
> >+
> > static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
> >                                  void __user *argp)
> > {
> >@@ -654,6 +670,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >       case VHOST_VDPA_GET_VQS_COUNT:
> >               r = vhost_vdpa_get_vqs_count(v, argp);
> >               break;
> >+      case VHOST_VDPA_SUSPEND:
> >+              r = vhost_vdpa_suspend(v);
> >+              break;
> >       default:
> >               r = vhost_dev_ioctl(&v->vdev, cmd, argp);
> >               if (r == -ENOIOCTLCMD)
> >diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> >index cab645d4a645..6d9f45163155 100644
> >--- a/include/uapi/linux/vhost.h
> >+++ b/include/uapi/linux/vhost.h
> >@@ -171,4 +171,18 @@
> > #define VHOST_VDPA_SET_GROUP_ASID     _IOW(VHOST_VIRTIO, 0x7C, \
> >                                            struct vhost_vring_state)
> >
> >+/* Suspend or resume a device so it does not process virtqueue requests anymore
> >+ *
> >+ * After the return of ioctl with suspend != 0, the device must finish any
> >+ * pending operations like in flight requests. It must also preserve all the
> >+ * necessary state (the virtqueue vring base plus the possible device specific
> >+ * states) that is required for restoring in the future. The device must not
> >+ * change its configuration after that point.
> >+ *
> >+ * After the return of ioctl with suspend == 0, the device can continue
> >+ * processing buffers as long as typical conditions are met (vq is enabled,
> >+ * DRIVER_OK status bit is enabled, etc).
> >+ */
> >+#define VHOST_VDPA_SUSPEND            _IOW(VHOST_VIRTIO, 0x7D, int)
>                                          ^
> IIUC we are not using the argument anymore, so this should be changed in
> _IO(VHOST_VIRTIO, 0x7D).
>
> And we should update a bit the documentation.
>

Totally right, replacing it for the next version.

Thanks!

> Thanks,
> Stefano
>