Re: [PULL 00/30] ppc-for-5.2 queue 20200904

[Laurent Vivier]

On 07/09/2020 18:29, Laurent Vivier wrote:
> On 07/09/2020 16:51, Cornelia Huck wrote:
>> On Mon, 7 Sep 2020 16:31:24 +0200
>> Laurent Vivier <lvivier@redhat.com> wrote:
>>
>>> On 07/09/2020 16:05, Philippe Mathieu-Daudé wrote:
>>>> Hi Thiago,
>>>>
>>>> On 9/7/20 3:29 PM, Laurent Vivier wrote:  
>>>>> On 07/09/2020 04:38, David Gibson wrote:  
>>>>>> On Sun, Sep 06, 2020 at 04:20:10PM +0100, Peter Maydell wrote:  
>>
>>>>>>> The 'check-tcg' tests for the linux-user static build also
>>>>>>> failed on an s390x test:
>>>>>>>
>>>>>>>   CHECK   debian-s390x-cross
>>>>>>>   BUILD   s390x-linux-user guest-tests with docker 
>>>>>>> qemu/debian-s390x-cross
>>>>>>>   RUN     tests for s390x
>>>>>>>   TEST    threadcount on s390x
>>>>>>> Unhandled trap: 0x10003  
>>>>>
>>>>> This is EXCP_HALTED (include/exec/cpu-all.h)
>>>>>
>>>>> The message error comes from cpu_loop() in linux-user/s390x/cpu_loop.c.
>>>>>
>>>>> The trap can only come from accel/tcg/cpu-exec.c
>>>>>
>>>>>     679 int cpu_exec(CPUState *cpu)
>>>>>     680 {
>>>>> ...
>>>>>     688     if (cpu_handle_halt(cpu)) {
>>>>>     689         return EXCP_HALTED;
>>>>>     690     }
>>>>>
>>>>> and
>>>>>
>>>>>     428 static inline bool cpu_handle_halt(CPUState *cpu)
>>>>>     429 {
>>>>>     430     if (cpu->halted) {
>>>>> ...
>>>>>     441         if (!cpu_has_work(cpu)) {
>>>>>     442             return true;
>>>>>     443         }
>>>>>
>>>>> and
>>>>>
>>>>>      58 static bool s390_cpu_has_work(CPUState *cs)
>>>>>      59 {
>>>>>      60     S390CPU *cpu = S390_CPU(cs);
>>>>>      61
>>>>>      62     /* STOPPED cpus can never wake up */
>>>>>      63     if (s390_cpu_get_state(cpu) != S390_CPU_STATE_LOAD &&
>>>>>      64         s390_cpu_get_state(cpu) != S390_CPU_STATE_OPERATING) {
>>>>>      65         return false;
>>>>>      66     }
>>>>>      67
>>>>>      68     if (!(cs->interrupt_request & CPU_INTERRUPT_HARD)) {
>>>>>      69         return false;
>>>>>      70     }
>>>>>      71
>>>>>      72     return s390_cpu_has_int(cpu);
>>>>>      73 }
>>>>>
>>>>> and in target/s390x/cpu.h:
>>>>>
>>>>>     772 #ifndef CONFIG_USER_ONLY
>>>>>     773 unsigned int s390_cpu_set_state(uint8_t cpu_state, S390CPU *cpu);
>>>>>     774 #else
>>>>>     775 static inline unsigned int s390_cpu_set_state(uint8_t cpu_state,
>>>>> S390CPU *cpu)
>>>>>     776 {
>>>>>     777     return 0;
>>>>>     778 }
>>>>>     779 #endif /* CONFIG_USER_ONLY */
>>>>>     780 static inline uint8_t s390_cpu_get_state(S390CPU *cpu)
>>>>>     781 {
>>>>>     782     return cpu->env.cpu_state;
>>>>>     783 }
>>>>>
>>>>> As cpu_state is never set, perhaps in case of linux-user it should
>>>>> always return S390_CPU_STATE_OPERATING?
>>
>> Possibly, we should not have any state handling for linux-user.
>>
> 
> I did that, but now 390_cpu_has_work() is false because
> CPU_INTERRUPT_HARD is not set in cs->interrupt_request.
> 
> I think we should not enter in cpu_loop() with halted set to 1.
> 
> Before the patch of this series, s390_cpu_reset() is called twice, and
> on the second call, halted is already 0.
> 
> With start_powered_off set to true in initfn, on the first reset
> "halted" is 0 and on the second it is 1 (because it has been copied from
> start_powered_off) and so cpu_loop() starts with halted set to 1 and fails.

What is happening:

[without start_powered_off]

  1- halted is set to 1 in s390x_cpu_initfn()
  2- halted is set to 0 in s390x_cpu_reset() by parent_reset()
     (cpu_common_reset()
  3- cpu_loop() is always entered with halted set to 0

[with start_powered_off]

  1- halted is set to start_powered_off (1) in s390x_cpu_reset() by
     parent_reset() (cpu_common_reset()
  2- cpu_loop() is always entered with halted set to 1

So in the first case, cpu_loop() is always started with halted set to 0
and in the second case with halted set to 1.

And I think, with linux-user, it should never be started with halted set
to 1.

We can't add a "#ifdef CONFIG_USER_ONLY" in hw/core/cpu.c to set halted
to 0 because it is in the common files, but we can do:

diff --git a/target/s390x/cpu.c b/target/s390x/cpu.c
index 73d7d6007e8e..749cd548f0f3 100644
--- a/target/s390x/cpu.c
+++ b/target/s390x/cpu.c
@@ -291,9 +291,9 @@ static void s390_cpu_initfn(Object *obj)
     S390CPU *cpu = S390_CPU(obj);

     cpu_set_cpustate_pointers(cpu);
-    cs->start_powered_off = true;
     cs->exception_index = EXCP_HLT;
 #if !defined(CONFIG_USER_ONLY)
+    cs->start_powered_off = true;
     object_property_add(obj, "crash-information", "GuestPanicInformation",
                         s390_cpu_get_crash_info_qom, NULL, NULL, NULL);
     cpu->env.tod_timer =

Thanks,
Laurent