Re: [Qemu-devel] [PATCH v2 1/2] spapr: disable hotplugging without OS

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

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On Thu, Jun 08, 2017 at 07:27:42PM +0200, Laurent Vivier wrote:
> If the OS is not started, QEMU sends an event to the OS
> that is lost and cannot be recovered. An unplug is not
> able to restore QEMU in a coherent state.
> So, while the OS is not started, disable CPU and memory hotplug.
> We guess the OS is started if the CAS has been negotiated.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

It seems a pain to introduce a whole new (migrated) variable just to
check this.  Could we instead tweak the allocation of spapr->ov5_cas,
so it is NULL until CAS is completed?

> ---
>  hw/ppc/spapr.c         | 51 +++++++++++++++++++++++++++++++++++++++++++++++---
>  hw/ppc/spapr_hcall.c   |  1 +
>  include/hw/ppc/spapr.h |  2 ++
>  3 files changed, 51 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 91b4057..4c979d5 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1308,6 +1308,7 @@ static void ppc_spapr_reset(void)
>  {
>      MachineState *machine = MACHINE(qdev_get_machine());
>      sPAPRMachineState *spapr = SPAPR_MACHINE(machine);
> +    sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(machine);
>      PowerPCCPU *first_ppc_cpu;
>      uint32_t rtas_limit;
>      hwaddr rtas_addr, fdt_addr;
> @@ -1373,6 +1374,7 @@ static void ppc_spapr_reset(void)
>      first_ppc_cpu->env.nip = SPAPR_ENTRY_POINT;
>  
>      spapr->cas_reboot = false;
> +    spapr->cas_completed = smc->cas_completed_default;

I also dislike the cas_completed_default thing.  If
cas_completed_default != false, it means that we will have
cas_completed == true when we have not, in fact, completed CAS.  I see
why you're doing this for migration compat, but that seems like a
recipe for confusion in the future.

>  }
>  
>  static void spapr_create_nvram(sPAPRMachineState *spapr)
> @@ -1528,6 +1530,27 @@ static const VMStateDescription vmstate_spapr_patb_entry = {
>      },
>  };
>  
> +static bool spapr_cas_completed_needed(void *opaque)
> +{
> +    sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(opaque);
> +
> +    /* we need to migrate cas_completed only if it is
> +     * not set by default
> +     */
> +    return !smc->cas_completed_default;
> +}
> +
> +static const VMStateDescription vmstate_spapr_cas_completed = {
> +    .name = "spapr_cas_completed",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = spapr_cas_completed_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_BOOL(cas_completed, sPAPRMachineState),
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
>  static const VMStateDescription vmstate_spapr = {
>      .name = "spapr",
>      .version_id = 3,
> @@ -1546,6 +1569,7 @@ static const VMStateDescription vmstate_spapr = {
>      .subsections = (const VMStateDescription*[]) {
>          &vmstate_spapr_ov5_cas,
>          &vmstate_spapr_patb_entry,
> +        &vmstate_spapr_cas_completed,
>          NULL
>      }
>  };
> @@ -2599,6 +2623,7 @@ out:
>  static void spapr_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>                                    Error **errp)
>  {
> +    sPAPRMachineState *ms = SPAPR_MACHINE(hotplug_dev);
>      PCDIMMDevice *dimm = PC_DIMM(dev);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
>      MemoryRegion *mr = ddc->get_memory_region(dimm);
> @@ -2617,6 +2642,14 @@ static void spapr_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>                     "Use 'memory-backend-file' with correct mem-path.");
>          return;
>      }
> +    if (dev->hotplugged) {
> +        if (!runstate_check(RUN_STATE_PRELAUNCH) &&
> +            !runstate_check(RUN_STATE_INMIGRATE) &&
> +            !ms->cas_completed) {
> +            error_setg(errp, "Memory hotplug not supported without OS");
> +            return;
> +        }
> +    }
>  }
>  
>  struct sPAPRDIMMState {
> @@ -2915,6 +2948,7 @@ static void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>                                  Error **errp)
>  {
>      MachineState *machine = MACHINE(OBJECT(hotplug_dev));
> +    sPAPRMachineState *ms = SPAPR_MACHINE(machine);
>      MachineClass *mc = MACHINE_GET_CLASS(hotplug_dev);
>      Error *local_err = NULL;
>      CPUCore *cc = CPU_CORE(dev);
> @@ -2923,9 +2957,18 @@ static void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>      CPUArchId *core_slot;
>      int index;
>  
> -    if (dev->hotplugged && !mc->has_hotpluggable_cpus) {
> -        error_setg(&local_err, "CPU hotplug not supported for this machine");
> -        goto out;
> +    if (dev->hotplugged) {
> +        if (!mc->has_hotpluggable_cpus) {
> +            error_setg(&local_err,
> +                       "CPU hotplug not supported for this machine");
> +            goto out;
> +        }
> +        if (!runstate_check(RUN_STATE_PRELAUNCH) &&
> +            !runstate_check(RUN_STATE_INMIGRATE) &&
> +            !ms->cas_completed) {
> +            error_setg(&local_err, "CPU hotplug not supported without OS");
> +            goto out;
> +        }
>      }
>  
>      if (strcmp(base_core_type, type)) {
> @@ -3358,9 +3401,11 @@ static void spapr_machine_2_9_instance_options(MachineState *machine)
>  
>  static void spapr_machine_2_9_class_options(MachineClass *mc)
>  {
> +    sPAPRMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
>      spapr_machine_2_10_class_options(mc);
>      SET_MACHINE_COMPAT(mc, SPAPR_COMPAT_2_9);
>      mc->numa_auto_assign_ram = numa_legacy_auto_assign_ram;
> +    smc->cas_completed_default = true;
>  }
>  
>  DEFINE_SPAPR_MACHINE(2_9, "2.9", false);
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index aa1ffea..d561a00 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1185,6 +1185,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
>          }
>      }
>  
> +    spapr->cas_completed = true;
>      return H_SUCCESS;
>  }
>  
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index f973b02..f5835db 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -57,6 +57,7 @@ struct sPAPRMachineClass {
>                            uint64_t *buid, hwaddr *pio, 
>                            hwaddr *mmio32, hwaddr *mmio64,
>                            unsigned n_dma, uint32_t *liobns, Error **errp);
> +    bool cas_completed_default;
>  };
>  
>  /**
> @@ -90,6 +91,7 @@ struct sPAPRMachineState {
>      sPAPROptionVector *ov5_cas;     /* negotiated (via CAS) option vectors */
>      bool cas_reboot;
>      bool cas_legacy_guest_workaround;
> +    bool cas_completed;
>  
>      Notifier epow_notifier;
>      QTAILQ_HEAD(, sPAPREventLogEntry) pending_events;

-- 
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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