Re: [Qemu-devel] [PATCH v4 6/6] spapr: fix migration of ICPState objects from/to older QEMU

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

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On Thu, Jun 08, 2017 at 03:43:27PM +0200, Greg Kurz wrote:
> Commit 5bc8d26de20c ("spapr: allocate the ICPState object from under
> sPAPRCPUCore") moved ICPState objects from the machine to CPU cores.
> This is an improvement since we no longer allocate ICPState objects
> that will never be used. But it has the side-effect of breaking
> migration of older machine types from older QEMU versions.
> 
> This patch allows spapr to register dummy "icp/server" entries to vmstate.
> These entries use a dedicated VMStateDescription that can swallow and
> discard state of an incoming migration stream, and that don't send anything
> on outgoing migration.
> 
> As for real ICPState objects, the instance_id is the cpu_index of the
> corresponding vCPU, which happens to be equal to the generated instance_id
> of older machine types.
> 
> The machine can unregister/register these entries when CPUs are dynamically
> plugged/unplugged.
> 
> This is only available for pseries-2.9 and older machines, thanks to a
> compat property.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> v4: - dropped paranoid g_assert()s
> ---
>  hw/ppc/spapr.c         |   86 +++++++++++++++++++++++++++++++++++++++++++++++-
>  include/hw/ppc/spapr.h |    2 +
>  2 files changed, 86 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index b2951d7618d6..1379986c0c7b 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -125,9 +125,50 @@ error:
>      return NULL;
>  }
>  
> +static bool pre_2_10_vmstate_dummy_icp_needed(void *opaque)
> +{
> +    return false;

Comment here with why always false makes sense here would be useful
for the future.

> +}
> +
> +static const VMStateDescription pre_2_10_vmstate_dummy_icp = {
> +    .name = "icp/server",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = pre_2_10_vmstate_dummy_icp_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UNUSED(4), /* uint32_t xirr */
> +        VMSTATE_UNUSED(1), /* uint8_t pending_priority */
> +        VMSTATE_UNUSED(1), /* uint8_t mfrr */
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
> +static void pre_2_10_vmstate_register_dummy_icp(sPAPRMachineState *spapr, int i)
> +{
> +    bool *flag = &spapr->pre_2_10_ignore_icp[i];

AFAICT you now set, but never check the flags in the ignore_icp array,
so you should be able to get rid of it.

> +    vmstate_register(NULL, i, &pre_2_10_vmstate_dummy_icp, flag);
> +    *flag = true;
> +}
> +
> +static void pre_2_10_vmstate_unregister_dummy_icp(sPAPRMachineState *spapr,
> +                                                  int i)
> +{
> +    bool *flag = &spapr->pre_2_10_ignore_icp[i];
> +
> +    vmstate_unregister(NULL, &pre_2_10_vmstate_dummy_icp, flag);
> +    *flag = false;
> +}
> +
> +static inline int xics_nr_servers(void)
> +{
> +    return DIV_ROUND_UP(max_cpus * kvmppc_smt_threads(), smp_threads);
> +}
> +
>  static void xics_system_init(MachineState *machine, int nr_irqs, Error **errp)
>  {
>      sPAPRMachineState *spapr = SPAPR_MACHINE(machine);
> +    sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(machine);
>  
>      if (kvm_enabled()) {
>          if (machine_kernel_irqchip_allowed(machine) &&
> @@ -149,6 +190,15 @@ static void xics_system_init(MachineState *machine, int nr_irqs, Error **errp)
>              return;
>          }
>      }
> +
> +    if (smc->pre_2_10_has_unused_icps) {
> +        int i;
> +
> +        spapr->pre_2_10_ignore_icp = g_malloc(xics_nr_servers());
> +        for (i = 0; i < xics_nr_servers(); i++) {
> +            pre_2_10_vmstate_register_dummy_icp(spapr, i);

A comment around here explaining that the dummy entries get
deregistered when real ICPs are registered would also be helpful.

> +        }
> +    }
>  }
>  
>  static int spapr_fixup_cpu_smt_dt(void *fdt, int offset, PowerPCCPU *cpu,
> @@ -977,7 +1027,6 @@ static void *spapr_build_fdt(sPAPRMachineState *spapr,
>      void *fdt;
>      sPAPRPHBState *phb;
>      char *buf;
> -    int smt = kvmppc_smt_threads();
>  
>      fdt = g_malloc0(FDT_MAX_SIZE);
>      _FDT((fdt_create_empty_tree(fdt, FDT_MAX_SIZE)));
> @@ -1017,7 +1066,7 @@ static void *spapr_build_fdt(sPAPRMachineState *spapr,
>      _FDT(fdt_setprop_cell(fdt, 0, "#size-cells", 2));
>  
>      /* /interrupt controller */
> -    spapr_dt_xics(DIV_ROUND_UP(max_cpus * smt, smp_threads), fdt, PHANDLE_XICP);
> +    spapr_dt_xics(xics_nr_servers(), fdt, PHANDLE_XICP);
>  
>      ret = spapr_populate_memory(spapr, fdt);
>      if (ret < 0) {
> @@ -2803,9 +2852,24 @@ static void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
>                                Error **errp)
>  {
>      MachineState *ms = MACHINE(qdev_get_machine());
> +    sPAPRMachineState *spapr = SPAPR_MACHINE(ms);
>      CPUCore *cc = CPU_CORE(dev);
>      CPUArchId *core_slot = spapr_find_cpu_slot(ms, cc->core_id, NULL);
>  
> +    if (spapr->pre_2_10_ignore_icp) {
> +        sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
> +        sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(cc));
> +        const char *typename = object_class_get_name(scc->cpu_class);
> +        size_t size = object_type_get_instance_size(typename);
> +        int i;
> +
> +        for (i = 0; i < cc->nr_threads; i++) {
> +            CPUState *cs = CPU(sc->threads + i * size);
> +
> +            pre_2_10_vmstate_register_dummy_icp(spapr, cs->cpu_index);
> +        }
> +    }
> +
>      assert(core_slot);
>      core_slot->cpu = NULL;
>      object_unparent(OBJECT(dev));
> @@ -2913,6 +2977,21 @@ static void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>          }
>      }
>      core_slot->cpu = OBJECT(dev);
> +
> +    if (spapr->pre_2_10_ignore_icp) {
> +        sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(cc));
> +        const char *typename = object_class_get_name(scc->cpu_class);
> +        size_t size = object_type_get_instance_size(typename);
> +        int i;
> +
> +        for (i = 0; i < cc->nr_threads; i++) {
> +            sPAPRCPUCore *sc = SPAPR_CPU_CORE(dev);
> +            void *obj = sc->threads + i * size;
> +
> +            cs = CPU(obj);
> +            pre_2_10_vmstate_unregister_dummy_icp(spapr, cs->cpu_index);
> +        }
> +    }
>  }
>  
>  static void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> @@ -3362,9 +3441,12 @@ 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->pre_2_10_has_unused_icps = true;
>  }
>  
>  DEFINE_SPAPR_MACHINE(2_9, "2.9", false);
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index f973b0284596..64382623199d 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -53,6 +53,7 @@ struct sPAPRMachineClass {
>      bool dr_lmb_enabled;       /* enable dynamic-reconfig/hotplug of LMBs */
>      bool use_ohci_by_default;  /* use USB-OHCI instead of XHCI */
>      const char *tcg_default_cpu; /* which (TCG) CPU to simulate by default */
> +    bool pre_2_10_has_unused_icps;
>      void (*phb_placement)(sPAPRMachineState *spapr, uint32_t index,
>                            uint64_t *buid, hwaddr *pio, 
>                            hwaddr *mmio32, hwaddr *mmio64,
> @@ -90,6 +91,7 @@ struct sPAPRMachineState {
>      sPAPROptionVector *ov5_cas;     /* negotiated (via CAS) option vectors */
>      bool cas_reboot;
>      bool cas_legacy_guest_workaround;
> +    bool *pre_2_10_ignore_icp;
>  
>      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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