Re: [PATCH 3/6] ppc: Reparent presenter objects to the interrupt controller object

[David Gibson]

On Wed, Oct 23, 2019 at 04:52:10PM +0200, Greg Kurz wrote:
> Each VCPU is associated to a presenter object within the interrupt
> controller, ie. TCTX for XIVE and ICP for XICS, but our current
> models put these objects below the VCPU, and we rely on CPU_FOREACH()
> to do anything that involves presenters.
> 
> This recently bit us with the CAM line matching logic in XIVE because
> CPU_FOREACH() can race with CPU hotplug and we ended up considering a
> VCPU that wasn't associated to a TCTX object yet. Other users of
> CPU_FOREACH() are 'info pic' for both XICS and XIVE. It is again very
> easy to crash QEMU with concurrent VCPU hotplug/unplug and 'info pic'.
> 
> Reparent the presenter objects to the corresponding interrupt controller
> object, ie. XIVE router or ICS, to make it clear they are not some extra
> data hanging from the CPU but internal XIVE or XICS entities. The CPU
> object now needs to explicitely take a reference on the presenter to
> ensure its pointer remains valid until unrealize time.
> 
> This will allow to get rid of CPU_FOREACH() and ease further improvements
> to the XIVE model.
> 
> This change doesn't impact section ids and is thus transparent to
> migration.
> 
> Signed-off-by: Greg Kurz <address@hidden>


Urgh.  I see why we want something like this, but reparenting the
presenters to the source modules (particularly for XICS) makes me
uncomfortable.

AFAICT the association here is *purely* about managing lifetimes, not
because those ICPs inherently have something to do with those ICSes.
Same with XIVE, although since they'll be on the same chip there's a
bit more logic to it.

For spapr we kinda-sorta treat the (single) ICS or XiveRouter object
as the "master" of the interrupt controller.  But that's not really
accurate to the hardware, so I don't really want to push that way of
looking at it any further than it already is.

If we could make the presenters children of the machine (spapr) or
chip (pnv) that might make more sense?

I'm also not totally convinced that having the presenter as a child of
the cpu is inherently bad.  Yes we have bugs now, but maybe the right
fix *is* actually to do the NULL check on every CPU_FOREACH().

For comparison, the lapic on x86 machines is a child of the cpu, and I
believe they do have NULL checks on cpu->apic_state in various places
they use CPU_FOREACH().

> ---
>  hw/intc/spapr_xive.c  |    6 +++++-
>  hw/intc/xics.c        |    7 +++++--
>  hw/intc/xics_spapr.c  |    8 ++++++--
>  hw/intc/xive.c        |    4 +++-
>  hw/ppc/pnv.c          |   17 +++++++++++++----
>  include/hw/ppc/xics.h |    2 +-
>  6 files changed, 33 insertions(+), 11 deletions(-)
> 
> diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
> index b09cc48bcb61..d74ee71e76b4 100644
> --- a/hw/intc/spapr_xive.c
> +++ b/hw/intc/spapr_xive.c
> @@ -526,6 +526,7 @@ static int 
> spapr_xive_cpu_intc_create(SpaprInterruptController *intc,
>          return -1;
>      }
>  
> +    object_ref(obj);
>      spapr_cpu->tctx = XIVE_TCTX(obj);
>      return 0;
>  }
> @@ -558,7 +559,10 @@ static void 
> spapr_xive_cpu_intc_reset(SpaprInterruptController *intc,
>  static void spapr_xive_cpu_intc_destroy(SpaprInterruptController *intc,
>                                          PowerPCCPU *cpu)
>  {
> -    xive_tctx_destroy(spapr_cpu_state(cpu)->tctx);
> +    XiveTCTX *tctx = spapr_cpu_state(cpu)->tctx;
> +
> +    object_unref(OBJECT(tctx));
> +    xive_tctx_destroy(tctx);
>  }
>  
>  static void spapr_xive_set_irq(SpaprInterruptController *intc, int irq, int 
> val)
> diff --git a/hw/intc/xics.c b/hw/intc/xics.c
> index 5f746079be46..d5e4db668a4b 100644
> --- a/hw/intc/xics.c
> +++ b/hw/intc/xics.c
> @@ -380,13 +380,16 @@ static const TypeInfo icp_info = {
>      .class_size = sizeof(ICPStateClass),
>  };
>  
> -Object *icp_create(Object *cpu, const char *type, XICSFabric *xi, Error 
> **errp)
> +Object *icp_create(Object *cpu, const char *type, ICSState *ics, XICSFabric 
> *xi,
> +                   Error **errp)
>  {
>      Error *local_err = NULL;
> +    g_autofree char *name = NULL;
>      Object *obj;
>  
>      obj = object_new(type);
> -    object_property_add_child(cpu, type, obj, &error_abort);
> +    name = g_strdup_printf("%s[%d]", type, CPU(cpu)->cpu_index);
> +    object_property_add_child(OBJECT(ics), name, obj, &error_abort);
>      object_unref(obj);
>      object_ref(OBJECT(xi));
>      object_property_add_const_link(obj, ICP_PROP_XICS, OBJECT(xi),
> diff --git a/hw/intc/xics_spapr.c b/hw/intc/xics_spapr.c
> index 5977d1bdb73f..080ed73aad64 100644
> --- a/hw/intc/xics_spapr.c
> +++ b/hw/intc/xics_spapr.c
> @@ -337,11 +337,12 @@ static int 
> xics_spapr_cpu_intc_create(SpaprInterruptController *intc,
>      Object *obj;
>      SpaprCpuState *spapr_cpu = spapr_cpu_state(cpu);
>  
> -    obj = icp_create(OBJECT(cpu), TYPE_ICP, ics->xics, errp);
> +    obj = icp_create(OBJECT(cpu), TYPE_ICP, ics, ics->xics, errp);
>      if (!obj) {
>          return -1;
>      }
>  
> +    object_ref(obj);
>      spapr_cpu->icp = ICP(obj);
>      return 0;
>  }
> @@ -355,7 +356,10 @@ static void 
> xics_spapr_cpu_intc_reset(SpaprInterruptController *intc,
>  static void xics_spapr_cpu_intc_destroy(SpaprInterruptController *intc,
>                                          PowerPCCPU *cpu)
>  {
> -    icp_destroy(spapr_cpu_state(cpu)->icp);
> +    ICPState *icp = spapr_cpu_state(cpu)->icp;
> +
> +    object_unref(OBJECT(icp));
> +    icp_destroy(icp);
>  }
>  
>  static int xics_spapr_claim_irq(SpaprInterruptController *intc, int irq,
> diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> index 952a461d5329..8d2da4a11163 100644
> --- a/hw/intc/xive.c
> +++ b/hw/intc/xive.c
> @@ -677,10 +677,12 @@ static const TypeInfo xive_tctx_info = {
>  Object *xive_tctx_create(Object *cpu, XiveRouter *xrtr, Error **errp)
>  {
>      Error *local_err = NULL;
> +    g_autofree char *name = NULL;
>      Object *obj;
>  
>      obj = object_new(TYPE_XIVE_TCTX);
> -    object_property_add_child(cpu, TYPE_XIVE_TCTX, obj, &error_abort);
> +    name = g_strdup_printf(TYPE_XIVE_TCTX "[%d]", CPU(cpu)->cpu_index);
> +    object_property_add_child(OBJECT(xrtr), name, obj, &error_abort);
>      object_unref(obj);
>      object_ref(cpu);
>      object_property_add_const_link(obj, "cpu", cpu, &error_abort);
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index bd17c3536dd5..cbeabf98bff6 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -767,14 +767,16 @@ static void pnv_chip_power8_intc_create(PnvChip *chip, 
> PowerPCCPU *cpu,
>      Error *local_err = NULL;
>      Object *obj;
>      PnvCPUState *pnv_cpu = pnv_cpu_state(cpu);
> +    Pnv8Chip *chip8 = PNV8_CHIP(chip);
>  
> -    obj = icp_create(OBJECT(cpu), TYPE_PNV_ICP, 
> XICS_FABRIC(qdev_get_machine()),
> -                     &local_err);
> +    obj = icp_create(OBJECT(cpu), TYPE_PNV_ICP, &chip8->psi.ics,
> +                     XICS_FABRIC(qdev_get_machine()), &local_err);

Here, the association of the ICPs with the PSI ICS is particularly arbitrary.

>      if (local_err) {
>          error_propagate(errp, local_err);
>          return;
>      }
>  
> +    object_ref(obj);
>      pnv_cpu->intc = obj;
>  }
>  
> @@ -788,7 +790,10 @@ static void pnv_chip_power8_intc_reset(PnvChip *chip, 
> PowerPCCPU *cpu)
>  
>  static void pnv_chip_power8_intc_destroy(PnvChip *chip, PowerPCCPU *cpu)
>  {
> -    icp_destroy(ICP(pnv_cpu_state(cpu)->intc));
> +    Object *intc = pnv_cpu_state(cpu)->intc;
> +
> +    object_unref(intc);
> +    icp_destroy(ICP(intc));
>  }
>  
>  /*
> @@ -825,6 +830,7 @@ static void pnv_chip_power9_intc_create(PnvChip *chip, 
> PowerPCCPU *cpu,
>          return;
>      }
>  
> +    object_ref(obj);
>      pnv_cpu->intc = obj;
>  }
>  
> @@ -837,7 +843,10 @@ static void pnv_chip_power9_intc_reset(PnvChip *chip, 
> PowerPCCPU *cpu)
>  
>  static void pnv_chip_power9_intc_destroy(PnvChip *chip, PowerPCCPU *cpu)
>  {
> -    xive_tctx_destroy(XIVE_TCTX(pnv_cpu_state(cpu)->intc));
> +    Object *intc = pnv_cpu_state(cpu)->intc;
> +
> +    object_unref(intc);
> +    xive_tctx_destroy(XIVE_TCTX(intc));
>  }
>  
>  /*
> diff --git a/include/hw/ppc/xics.h b/include/hw/ppc/xics.h
> index 48a75aa4ab75..f4827e748fd8 100644
> --- a/include/hw/ppc/xics.h
> +++ b/include/hw/ppc/xics.h
> @@ -179,7 +179,7 @@ void ics_pic_print_info(ICSState *ics, Monitor *mon);
>  void ics_resend(ICSState *ics);
>  void icp_resend(ICPState *ss);
>  
> -Object *icp_create(Object *cpu, const char *type, XICSFabric *xi,
> +Object *icp_create(Object *cpu, const char *type, ICSState *ics, XICSFabric 
> *xi,
>                     Error **errp);
>  void icp_destroy(ICPState *icp);
>  
> 

-- 
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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