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

[Greg Kurz]

On Wed, 17 Jul 2019 15:39:52 +1000
Nicholas Piggin <address@hidden> 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 <address@hidden>
> ---
> 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...

> +    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() ?

> +}
> +
>  static target_ulong h_confer(PowerPCCPU *cpu, SpaprMachineState *spapr,
>                             target_ulong opcode, target_ulong *args)
>  {
> @@ -1979,6 +2021,9 @@ static void hypercall_register_types(void)
>      spapr_register_hypercall(H_CONFER, h_confer);
>      spapr_register_hypercall(H_PROD, h_prod);
>  
> +    /* hcall-join */
> +    spapr_register_hypercall(H_JOIN, h_join);
> +
>      spapr_register_hypercall(H_SIGNAL_SYS_RESET, h_signal_sys_reset);
>  
>      /* processor register resource access h-calls */