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

[Greg Kurz]

On Mon, 12 Jun 2017 22:21:48 +0800
David Gibson <address@hidden> wrote:

> 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 <address@hidden>
> > ---
> > 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.
> 

Ok.

> > +}
> > +
> > +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.
> 

As explained in another mail, I need to pass a unique (void *) argument
to vmstate_register() and vmstate_unregister(). But I could also pass
(void*) i, in which case I could get rid of the array indeed.

> > +    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.
> 

Ok.

> > +        }
> > +    }
> >  }
> >  
> >  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;
> >   
>

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