On Wed, Jun 1, 2022 at 9:13 PM Parav Pandit [off-list ref] wrote:

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From: Eugenio Perez Martin <eperezma@redhat.com>
Sent: Wednesday, June 1, 2022 7:15 AM

On Wed, Jun 1, 2022 at 1:03 PM Michael S. Tsirkin [off-list ref] wrote:

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On Thu, May 26, 2022 at 02:43:37PM +0200, Eugenio Pérez wrote:

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The ioctl adds support for stop the device from userspace.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 drivers/vhost/vdpa.c       | 18 ++++++++++++++++++
 include/uapi/linux/vhost.h | 14 ++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index

32713db5831d..d1d19555c4b7 100644

--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c

@@ -478,6 +478,21 @@ static long vhost_vdpa_get_vqs_count(struct

vhost_vdpa *v, u32 __user *argp)

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      return 0;
 }

+static long vhost_vdpa_stop(struct vhost_vdpa *v, u32 __user *argp)
+{
+     struct vdpa_device *vdpa = v->vdpa;
+     const struct vdpa_config_ops *ops = vdpa->config;
+     int stop;
+
+     if (!ops->stop)
+             return -EOPNOTSUPP;
+
+     if (copy_from_user(&stop, argp, sizeof(stop)))
+             return -EFAULT;
+
+     return ops->stop(vdpa, stop);
+}
+
 static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int

cmd,

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                                 void __user *argp)  { @@ -650,6
+665,9 @@ 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_STOP:
+             r = vhost_vdpa_stop(v, argp);
+             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..c7e47b29bf61 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,

\

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                                           struct vhost_vring_state)

+/* Stop or resume a device so it does not process virtqueue
+requests anymore
+ *
+ * After the return of ioctl with stop != 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 stop == 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_STOP                      _IOW(VHOST_VIRTIO, 0x7D, int)
+

A better name is VHOST_VDPA_SET_STATE
State = stop/suspend
State = start/resume

Suspend/resume seems more logical, as opposed start/stop, because it more clearly indicates that the resume (start) is from some programmed beginning (and not first boot).

It's fine to move to that nomenclature in my opinion.

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 #endif

I wonder how does this interact with the admin vq idea.
I.e. if we stop all VQs then apparently admin vq can't work either ...
Thoughts?

Copying here the answer to Parav, feel free to answer to any thread or
highlight if I missed something :). Using the admin vq proposal terminology of
"device group".

--
This would stop a device of a device
group, but not the whole virtqueue group. If the admin VQ is offered by the
PF (since it's not exposed to the guest), it will continue accepting requests as
normal. If it's exposed in the VF, I think the best bet is to shadow it, since
guest and host requests could conflict.

vhost-vdpa device is exposed for a VF through vp-vdpa driver to user land.
Now vp-vdpa driver will have to choose between using config register vs using AQ to suspend/resume the device.

vp_vdpa cannot choose if the virtio device has an admin vq or any
other feature, it just wraps the virtio device. If that virtio device
does not expose AQ, vp_vdpa cannot expose it.

Why not always begin with more superior interface of AQ that address multiple of these needs for LM case?

Because it doesn't address valid use cases like vp_vdpa with no AQ,
devices that are not VF, or nested virtualization.

VHOST_VDPA_STOP / VHOST_VDPA_SET_STATE does not replace AQ commands:
It's just the way vhost-vdpa exposes that capability to qemu. vdpa
backend is free to choose whatever methods it finds better to
implement it.

For LM case, more you explore, we realize that either VF relying on PF's AQ for query/config/setup/restore makes more sense or have its own dedicated AQ.

This ioctl does not mandate that the device cannot implement it
through AQ, or that the device has to be a VF.

Thanks!

VM's suspend/resume operation can be handled through the shadow Q.

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Since this is offered through vdpa, the device backend driver can route it to
whatever method works better for the hardware. For example, to send an
admin vq command to the PF. That's why it's important to keep the feature
as self-contained and orthogonal to others as possible.
--

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--
2.31.1