[PATCH v2 0/1] pSeries: handle hotunplug errors in drc_unisolate_logical()

[Daniel Henrique Barboza]

Changes from v1:
- added more context in the commit message
- added David's R-b
v1 link: https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg03145.html 

Hi,

This is the QEMU side of a kernel change being proposed in [1],
where an attempt to implement a CPU hotunplug error report
mechanism was proposed.

The idea was discussed first in this mailing list [2], where the
RTAS set-indicator call would be used to signal QEMU when a kernel
side error happens during the unplug process.

Using the modified kernel and this patch, this is the result of a
failed CPU hotunplug attempt when trying to unplug the last online
CPU of the guest:

( QEMU command line: qemu-system-ppc64 -machine pseries,accel=kvm,usb=off
-smp 1,maxcpus=2,threads=1,cores=2,sockets=1 ... )

[root@localhost ~]# QEMU 5.2.92 monitor - type 'help' for more information
(qemu) device_add host-spapr-cpu-core,core-id=1,id=core1
(qemu) 

[root@localhost ~]# echo 0 > /sys/devices/system/cpu/cpu0/online
[   77.548442][   T13] IRQ 19: no longer affine to CPU0
[   77.548452][   T13] IRQ 20: no longer affine to CPU0
[   77.548458][   T13] IRQ 256: no longer affine to CPU0
[   77.548465][   T13] IRQ 258: no longer affine to CPU0
[   77.548472][   T13] IRQ 259: no longer affine to CPU0
[   77.548479][   T13] IRQ 260: no longer affine to CPU0
[   77.548485][   T13] IRQ 261: no longer affine to CPU0
[   77.548590][    T0] cpu 0 (hwid 0) Ready to die...
[root@localhost ~]# (qemu) 
(qemu) device_del core1
(qemu) [   83.214073][  T100] pseries-hotplug-cpu: Failed to offline CPU 
PowerPC,POWER9, rc: -16
qemu-system-ppc64: Device hotunplug rejected by the guest for device core1

(qemu) 


As mentioned in the kernel change, if this is accepted I'll push
for a PAPR change to make this an official device removal error
report mechanism.


[1] 
https://lore.kernel.org/linuxppc-dev/20210416210216.380291-3-danielhb413@gmail.com/
[2] https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg06395.html

Daniel Henrique Barboza (1):
  spapr_drc.c: handle hotunplug errors in drc_unisolate_logical()

 hw/ppc/spapr_drc.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

-- 
2.30.2