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

[Laurent Vivier]

On 14/08/2015 07:20, Bharata B Rao wrote:
> 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()

It doesn't work for PCI, because (QEMU 2.4.0):

static int set_allocation_state(sPAPRDRConnector *drc,
                                sPAPRDRAllocationState state)
...
    if (drc->type != SPAPR_DR_CONNECTOR_TYPE_PCI) {
...
            drck->detach(drc, DEVICE(drc->dev), drc->detach_cb,
                         drc->detach_cb_opaque, NULL);
...
    }

> - drck->detach() now calls drc->detach_cb() that truly releases the
>   CPU resource by getting rid of vCPU thread in QEMU.

Laurent