Re: [Qemu-devel] [PATCH RFC] pseries: define coldplugged devices as "configured"

[Bharata B Rao]

On Thu, Aug 13, 2015 at 02:53:02PM +0200, Laurent Vivier wrote:
> When a device is hotplugged, attach() sets "configured" to
> false, waiting an action from the OS to configure it and then
> to call ibm,configure-connector. On ibm,configure-connector,
> the hypervisor sets "configured" to true.
> 
> In case of coldplugged device, attach() sets "configured" to
> false, but firmware and OS never call the ibm,configure-connector
> in this case, so it remains set to false.
> 
> It could be harmless, but when we unplug a device, hypervisor
> waits the device becomes configured because for it, a not configured
> device is a device being configured, so it waits the end of configuration
> to unplug it... and it never happens, so it is never unplugged.

Not true for at least logical DR device like CPU. I am able to cleanly
unplug a cold plugged CPU in the patchset I posted at:

https://lists.gnu.org/archive/html/qemu-ppc/2015-08/msg00041.html

And this is how the state transitions work for cold plugged CPU devices:

- Cold plugged CPU DRC is explicitly set with allocation_state=USABLE
  and isolation_state=UNISOLATED.
- device_del results in drck->detach() that just returns by setting
  drc->awaiting_release to true.
- Unplug notification is sent to guest.
- Guest comes back with set_indicator RTAS call for setting isolation_state
  to ISOLATED. set_isolation_state() sets drc->configured to false.
- Guest comes back again with set_indicator RTAS call for setting allocation
  state to UNUSABLE. set_allocation_state() finalizes the device removal by
  calling drck->detach()
- drck->detach() now calls drc->detach_cb() that truly releases the
  CPU resource by getting rid of vCPU thread in QEMU.

Regards,
Bharata.