[PATCH v8 0/3] Implement vdpasim suspend operation

["Eugenio Pérez" <eperezma@redhat.com>]

Implement suspend operation for vdpa_sim devices, so vhost-vdpa will offer
that backend feature and userspace can effectively suspend the device.

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 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 virtqueue buffers.

In the future, we will provide features similar to
VHOST_USER_GET_INFLIGHT_FD so the device can save pending operations.

Applied on top of vhost branch.

Comments are welcome.

v8:
* v7 but incremental from vhost instead of isolated.

v7:
* Remove ioctl leftover argument and update doc accordingly.

v6:
* Remove the resume operation, making the ioctl simpler. We can always add
  another ioctl for VM_STOP/VM_RESUME operation later.
* s/stop/suspend/ to differentiate more from reset.
* Clarify scope of the suspend operation.

v5:
* s/not stop/resume/ in doc.

v4:
* Replace VHOST_STOP to VHOST_VDPA_STOP in vhost ioctl switch case too.

v3:
* s/VHOST_STOP/VHOST_VDPA_STOP/
* Add documentation and requirements of the ioctl above its definition.

v2:
* Replace raw _F_STOP with BIT_ULL(_F_STOP).
* Fix obtaining of stop ioctl arg (it was not obtained but written).
* Add stop to vdpa_sim_blk.

[1] git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git

Eugenio Pérez (3):
  vdpa: delete unreachable branch on vdpasim_suspend
  vdpa: Remove wrong doc of VHOST_VDPA_SUSPEND ioctl
  vhost: Remove invalid parameter of VHOST_VDPA_SUSPEND ioctl

 drivers/vdpa/vdpa_sim/vdpa_sim.c |  7 -------
 include/linux/vdpa.h             |  2 +-
 include/uapi/linux/vhost.h       | 17 ++++++-----------
 3 files changed, 7 insertions(+), 19 deletions(-)

-- 
2.31.1