Re: [PATCH for-6.0 4/9] spapr: Set compat mode in spapr_reset_vcpu()

[David Gibson]

On Sat, Nov 21, 2020 at 12:42:03AM +0100, Greg Kurz wrote:
> When it comes to resetting the compat mode of the vCPUS, there are
> two situations to consider:
> (1) machine reset should set the compat mode back to the machine default,
>     ie. spapr->max_compat_pvr
> (2) hot plugged vCPUs should set their compat mode to mach the boot vCPU,
>     ie. POWERPC_CPU(first_cpu)->compat_pvr
> 
> This is currently handled in two separate places: globally for all vCPUs
> from the machine reset code for (1) and for each thread of a core from
> the hotplug path for (2).
> 
> Since the machine reset code already resets all vCPUs, starting with boot
> vCPU, consolidate the logic in spapr_reset_vcpu(). Special case the boot
> vCPU so that it resets its compat mode back to the machine default. Any
> other vCPU just need to match the compat mode of the boot vCPU.
> 
> Failing to set the compat mode during machine reset is a fatal error,
> but not for hot plugged vCPUs. This is arguable because if we've been
> able to set the boot vCPU compat mode at CAS or during machine reset,
> it should definitely not fail for other vCPUs. Since spapr_reset_vcpu()
> already has a fatal error path for kvm_check_mmu() failures, do the
> same for ppc_set_compat().
> 
> This gets rid of an error path in spapr_core_plug(). It will allow
> further simplifications.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>  hw/ppc/spapr.c          | 16 ----------------
>  hw/ppc/spapr_cpu_core.c | 13 +++++++++++++
>  2 files changed, 13 insertions(+), 16 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index f58f77389e8e..da7586f548df 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1606,8 +1606,6 @@ static void spapr_machine_reset(MachineState *machine)
>      spapr_ovec_cleanup(spapr->ov5_cas);
>      spapr->ov5_cas = spapr_ovec_new();
>  
> -    ppc_set_compat_all(spapr->max_compat_pvr, &error_fatal);
> -
>      /*
>       * This is fixing some of the default configuration of the XIVE
>       * devices. To be called after the reset of the machine devices.
> @@ -3785,20 +3783,6 @@ static void spapr_core_plug(HotplugHandler 
> *hotplug_dev, DeviceState *dev,
>  
>      core_slot->cpu = OBJECT(dev);
>  
> -    /*
> -     * Set compatibility mode to match the boot CPU, which was either set
> -     * by the machine reset code or by CAS.
> -     */
> -    if (hotplugged) {
> -        for (i = 0; i < cc->nr_threads; i++) {
> -            if (ppc_set_compat(core->threads[i],
> -                               POWERPC_CPU(first_cpu)->compat_pvr,
> -                               errp) < 0) {
> -                return;
> -            }
> -        }
> -    }
> -
>      if (smc->pre_2_10_has_unused_icps) {
>          for (i = 0; i < cc->nr_threads; i++) {
>              cs = CPU(core->threads[i]);
> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> index 2f7dc3c23ded..17741a3fb77f 100644
> --- a/hw/ppc/spapr_cpu_core.c
> +++ b/hw/ppc/spapr_cpu_core.c
> @@ -27,6 +27,7 @@
>  
>  static void spapr_reset_vcpu(PowerPCCPU *cpu)
>  {
> +    PowerPCCPU *first_ppc_cpu = POWERPC_CPU(first_cpu);
>      CPUState *cs = CPU(cpu);
>      CPUPPCState *env = &cpu->env;
>      PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
> @@ -69,6 +70,18 @@ static void spapr_reset_vcpu(PowerPCCPU *cpu)
>      kvm_check_mmu(cpu, &error_fatal);
>  
>      spapr_irq_cpu_intc_reset(spapr, cpu);
> +
> +    /*
> +     * The boot CPU is only reset during machine reset : reset its
> +     * compatibility mode to the machine default. For other CPUs,
> +     * either cold plugged or hot plugged, set the compatibility mode
> +     * to match the boot CPU, which was either set by the machine reset
> +     * code or by CAS.
> +     */
> +    ppc_set_compat(cpu,
> +                   cpu == first_ppc_cpu ?
> +                   spapr->max_compat_pvr : first_ppc_cpu->compat_pvr,
> +                   &error_fatal);

This assumes that when it is called for a non-boot CPU, it has already
been called for the boot CPU..  Are we certain that's guaranteed by
the sequence of reset calls during a full machine reset?

>  }
>  
>  void spapr_cpu_set_entry_state(PowerPCCPU *cpu, target_ulong nip,

-- 
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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