Re: [Qemu-devel] [PATCH v5 4/4] spapr: Implement H_JOIN

[Nicholas Piggin <npiggin@gmail.com>]

Greg Kurz's on July 18, 2019 3:30 am:
> On Wed, 17 Jul 2019 15:39:52 +1000
> Nicholas Piggin <npiggin@gmail.com> wrote:
> 
>> This has been useful to modify and test the Linux pseries suspend
>> code but it requires modification to the guest to call it (due to
>> being gated by other unimplemented features). It is not otherwise
>> used by Linux yet, but work is slowly progressing there.
>> 
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>> Changes since v4:
>> - Style
>> 
>>  hw/ppc/spapr.c       |  1 +
>>  hw/ppc/spapr_hcall.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 46 insertions(+)
>> 
>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>> index 13c423347e..59cd24f9c3 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -1066,6 +1066,7 @@ static void spapr_dt_rtas(SpaprMachineState *spapr, void *fdt)
>>      add_str(hypertas, "hcall-tce");
>>      add_str(hypertas, "hcall-vio");
>>      add_str(hypertas, "hcall-splpar");
>> +    add_str(hypertas, "hcall-join");
>>      add_str(hypertas, "hcall-bulk");
>>      add_str(hypertas, "hcall-set-mode");
>>      add_str(hypertas, "hcall-sprg0");
>> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
>> index 5e655172b2..57c1ee0fe1 100644
>> --- a/hw/ppc/spapr_hcall.c
>> +++ b/hw/ppc/spapr_hcall.c
>> @@ -1069,6 +1069,48 @@ static target_ulong h_cede(PowerPCCPU *cpu, SpaprMachineState *spapr,
>>      return H_SUCCESS;
>>  }
>>  
>> +static target_ulong h_join(PowerPCCPU *cpu, SpaprMachineState *spapr,
>> +                           target_ulong opcode, target_ulong *args)
>> +{
>> +    CPUPPCState *env = &cpu->env;
>> +    CPUState *cs;
>> +    SpaprCpuState *spapr_cpu = spapr_cpu_state(cpu);
>> +    bool last_unjoined = true;
>> +
>> +    if (env->msr & (1ULL << MSR_EE)) {
>> +        return H_BAD_MODE;
>> +    }
>> +
>> +    if (spapr_cpu->prod) {
>> +        spapr_cpu->prod = false;
>> +        return H_SUCCESS;
>> +    }
>> +
> 
> PAPR says that H_JOIN "performs the equivalent of a H_CONFER (proc=self)",
> unless called by the last unjoined thread, in which case H_CONTINUE
> should be returned. It thus seems that the spapr_cpu->prod check should
> be done after the loop below otherwise if the last active thread was
> just prodded (can happen?), it won't return the expected value, and...

Good lawyering, I would say you are right.

>> +    CPU_FOREACH(cs) {
>> +        PowerPCCPU *c = POWERPC_CPU(cs);
>> +        CPUPPCState *e = &c->env;
>> +        if (c == cpu) {
>> +            continue;
>> +        }
>> +
>> +        /* Don't have a way to indicate joined, so use halted && MSR[EE]=0 */
>> +        if (!cs->halted || (e->msr & (1ULL << MSR_EE))) {
>> +            last_unjoined = false;
>> +            break;
>> +        }
>> +    }
>> +    if (last_unjoined) {
>> +        return H_CONTINUE;
>> +    }
>> +
>> +    cs = CPU(cpu);
>> +    cs->halted = 1;
>> +    cs->exception_index = EXCP_HALTED;
>> +    cs->exit_request = 1;
>> +
>> +    return H_SUCCESS;
> 
> ... then, you can maybe factor out this code to an h_confer_self()
> helper to be called by h_join() and h_confer() ?

I'll take a look.

Thanks,
Nick