[Qemu-devel] [Bug 1739413] [NEW] Hotplugged vcpu does not guarantee cpu compat mode(power8) on power9 host

[Satheesh Rajendran]

Public bug reported:

./ppc64-softmmu/qemu-system-ppc64 -version
QEMU emulator version 2.11.50 (v2.11.0-254-gaf35267)

1. Boot a power8 compat mode guest power9 HW.
./ppc64-softmmu/qemu-system-ppc64 -machine 
pseries,accel=kvm,max-cpu-compat=power8 -m 4096 /home/sath/images/guest.qcow2 
-smp 1,maxcpus=2 -serial /dev/pts/8  -monitor stdio -vga none -nographic
QEMU 2.11.50 monitor - type 'help' for more information
(qemu) 

2. Check for cpuinfo

# cat /proc/cpuinfo 
processor       : 0
cpu             : POWER8 (architected), altivec supported
clock           : 2200.000000MHz
revision        : 2.1 (pvr 004e 1201)

timebase        : 512000000
platform        : pSeries
model           : IBM pSeries (emulated by qemu)
machine         : CHRP IBM pSeries (emulated by qemu)
MMU             : Hash


3. Run a small program invoking isa v3.0 instruction, it should complain 
'Illegal instruction' as it is a power8 compat guest
# cat 1.c 
#include <stdio.h>
void main()
    {
    asm volatile (".long 0x7c0005e6");
    }
# ./a.out 
[   59.352795] a.out[1741]: unhandled signal 4 at 0000000010000600 nip 
0000000010000600 lr 00007fffb4da5080 code 1
Illegal instruction 

4. Hotplug a vcpu
(qemu) device_add host-spapr-cpu-core,id=core1,core-id=1
(qemu) info cpus
* CPU #0: nip=0xc0000000000de42c thread_id=113110
  CPU #1: nip=0xc0000000000de42c thread_id=113348

5. Try running the same program in the hotplugged vcpu and it does not
complain as 'Illegal instruction'

#taskset -c 1 ./a.out ----------------------NOK
#  

# taskset -c 0 ./a.out 
[  356.618031] a.out[1755]: unhandled signal 4 at 0000000010000600 nip 
0000000010000600 lr 00007fffae7f5080 code 1
Illegal instruction

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: ppc64le

** Summary changed:

- Hotplugged vcpu does not guarantee cpu compat mode
+ Hotplugged vcpu does not guarantee cpu compat mode(power8) on power9 host

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https://bugs.launchpad.net/bugs/1739413

Title:
  Hotplugged vcpu does not guarantee cpu compat mode(power8) on power9
  host

Status in QEMU:
  New

Bug description:
  ./ppc64-softmmu/qemu-system-ppc64 -version
  QEMU emulator version 2.11.50 (v2.11.0-254-gaf35267)

  1. Boot a power8 compat mode guest power9 HW.
  ./ppc64-softmmu/qemu-system-ppc64 -machine 
pseries,accel=kvm,max-cpu-compat=power8 -m 4096 /home/sath/images/guest.qcow2 
-smp 1,maxcpus=2 -serial /dev/pts/8  -monitor stdio -vga none -nographic
  QEMU 2.11.50 monitor - type 'help' for more information
  (qemu) 

  2. Check for cpuinfo

  # cat /proc/cpuinfo 
  processor     : 0
  cpu           : POWER8 (architected), altivec supported
  clock         : 2200.000000MHz
  revision      : 2.1 (pvr 004e 1201)

  timebase      : 512000000
  platform      : pSeries
  model         : IBM pSeries (emulated by qemu)
  machine               : CHRP IBM pSeries (emulated by qemu)
  MMU           : Hash

  
  3. Run a small program invoking isa v3.0 instruction, it should complain 
'Illegal instruction' as it is a power8 compat guest
  # cat 1.c 
  #include <stdio.h>
  void main()
      {
      asm volatile (".long 0x7c0005e6");
      }
  # ./a.out 
  [   59.352795] a.out[1741]: unhandled signal 4 at 0000000010000600 nip 
0000000010000600 lr 00007fffb4da5080 code 1
  Illegal instruction 

  4. Hotplug a vcpu
  (qemu) device_add host-spapr-cpu-core,id=core1,core-id=1
  (qemu) info cpus
  * CPU #0: nip=0xc0000000000de42c thread_id=113110
    CPU #1: nip=0xc0000000000de42c thread_id=113348

  5. Try running the same program in the hotplugged vcpu and it does not
  complain as 'Illegal instruction'

  #taskset -c 1 ./a.out ----------------------NOK
  #  

  # taskset -c 0 ./a.out 
  [  356.618031] a.out[1755]: unhandled signal 4 at 0000000010000600 nip 
0000000010000600 lr 00007fffae7f5080 code 1
  Illegal instruction

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