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

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Sep 07, 2020 at 09:46:28PM +0200, Philippe Mathieu-Daudé wrote:
> On 9/7/20 7:26 PM, Laurent Vivier wrote:
> > 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 =
> 
> This looks like the correct fix indeed :)
> (Maybe worth adding a comment around).
> 
> Thanks for investigating!

Yes, thanks for figuring this out.  I'll fix up my PR accordingly and
resend today.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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