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SubjectRe: [PATCH v6 3/4] vhost-vdpa: uAPI to suspend the device
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@redhat.com>
>---
> 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.

Thanks,
Stefano

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