Re: [Qemu-devel] [PATCH v2] spapr: add splpar hcalls H_JOIN, H_PROD, H_CONFER

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

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On Fri, Apr 12, 2019 at 07:36:03PM +1000, Nicholas Piggin wrote:
> These implementations have a few deficiencies that are noted, but are
> good enough for Linux to use.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
> 
> Cleaned up checkpatch warnings, sorry I didn't realise that exists.
> 
>  hw/ppc/spapr_hcall.c | 88 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 88 insertions(+)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 8a736797b9..e985bb694d 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1065,6 +1065,90 @@ 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 = CPU(cpu);
> +
> +    if (env->msr & (1ULL << MSR_EE)) {
> +        return H_BAD_MODE;
> +    }
> +
> +    /*
> +     * This should check for single-threaded mode. In practice, Linux
> +     * does not try to H_JOIN all CPUs.
> +     */
> +
> +    cs->halted = 1;
> +    cs->exception_index = EXCP_HALTED;
> +    cs->exit_request = 1;
> +
> +    return H_SUCCESS;
> +}
> +
> +static target_ulong h_confer(PowerPCCPU *cpu, SpaprMachineState *spapr,
> +                           target_ulong opcode, target_ulong *args)
> +{
> +    target_long target = args[0];
> +    CPUState *cs = CPU(cpu);
> +
> +    /*
> +     * This does not do a targeted yield or confer, but check the parameter
> +     * anyway. -1 means confer to all/any other CPUs.
> +     */
> +    if (target != -1 && !CPU(spapr_find_cpu(target))) {
> +        return H_PARAMETER;
> +    }
> +
> +    /*
> +     * H_CONFER with target == this is not exactly the same as H_JOIN
> +     * according to PAPR (e.g., MSR[EE] check and single threaded check
> +     * is not done in this case), but unlikely to matter.
> +     */
> +    if (cpu == spapr_find_cpu(target)) {
> +        return h_join(cpu, spapr, opcode, args);
> +    }
> +
> +    /*
> +     * This does not implement the dispatch sequence check that PAPR calls for,
> +     * but PAPR also specifies a stronger implementation where the target must
> +     * be run (or EE, or H_PROD) before H_CONFER returns. Without such a hard
> +     * scheduling requirement implemented, there is no correctness reason to
> +     * implement the dispatch sequence check.
> +     */
> +    cs->exception_index = EXCP_YIELD;
> +    cpu_loop_exit(cs);
> +
> +    return H_SUCCESS;
> +}
> +
> +/*
> + * H_PROD and H_CONFER are specified to only modify GPR r3, which is not
> + * achievable running under KVM,

Uh.. why not?

> although KVM already implements H_CONFER
> + * this way.

And this seems to contradict the above.

> + */
> +static target_ulong h_prod(PowerPCCPU *cpu, SpaprMachineState *spapr,
> +                           target_ulong opcode, target_ulong *args)
> +{
> +    target_long target = args[0];
> +    CPUState *cs;
> +
> +    /*
> +     * Should set the prod flag in the VPA.

So.. why doesn't it?

> +     */
> +
> +    cs = CPU(spapr_find_cpu(target));
> +    if (!cs) {
> +        return H_PARAMETER;
> +    }
> +
> +    cs->halted = 0;
> +    qemu_cpu_kick(cs);
> +
> +    return H_SUCCESS;
> +}
> +
>  static target_ulong h_rtas(PowerPCCPU *cpu, SpaprMachineState *spapr,
>                             target_ulong opcode, target_ulong *args)
>  {
> @@ -1860,6 +1944,10 @@ static void hypercall_register_types(void)
>      /* hcall-splpar */
>      spapr_register_hypercall(H_REGISTER_VPA, h_register_vpa);
>      spapr_register_hypercall(H_CEDE, h_cede);
> +    spapr_register_hypercall(H_CONFER, h_confer);
> +    spapr_register_hypercall(H_JOIN, h_join);

I don't see any sign that H_JOIN is implemented in KVM, although
H_CONFER and H_PROD certainly are.

> +    spapr_register_hypercall(H_PROD, h_prod);
> +
>      spapr_register_hypercall(H_SIGNAL_SYS_RESET, h_signal_sys_reset);
>  
>      /* processor register resource access h-calls */

Don't we also need to add something to hypertas-calls to advertise the
availability of these calls to the guest?

-- 
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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