Re: [Qemu-devel] [PATCH v3 2/3] exec: rename cpu_exec_init() as cpu_exec_realizefn()

[Andrew Jones]

On Mon, Oct 17, 2016 at 05:20:22PM -0200, Eduardo Habkost wrote:
> On Sat, Oct 15, 2016 at 12:52:48AM +0200, Laurent Vivier wrote:
> > Modify all CPUs to call it from XXX_cpu_realizefn() function.
> > 
> > Remove all the cannot_destroy_with_object_finalize_yet as
> > unsafe references have been moved to cpu_exec_realizefn().
> > (tested with QOM command provided by commit 4c315c27)
> > 
> > for arm:
> > 
> > Setting of cpu->mp_affinity is moved from arm_cpu_initfn()
> > to arm_cpu_realizefn() as setting of cpu_index is now done
> > in cpu_exec_realizefn().
> > 
> > Signed-off-by: Laurent Vivier <address@hidden>
> [...]
> > diff --git a/target-arm/cpu.c b/target-arm/cpu.c
> > index 1b9540e..364a45d 100644
> > --- a/target-arm/cpu.c
> > +++ b/target-arm/cpu.c
> > @@ -441,22 +441,11 @@ static void arm_cpu_initfn(Object *obj)
> >      CPUState *cs = CPU(obj);
> >      ARMCPU *cpu = ARM_CPU(obj);
> >      static bool inited;
> > -    uint32_t Aff1, Aff0;
> >  
> >      cs->env_ptr = &cpu->env;
> > -    cpu_exec_init(cs, &error_abort);
> >      cpu->cp_regs = g_hash_table_new_full(g_int_hash, g_int_equal,
> >                                           g_free, g_free);
> >  
> > -    /* This cpu-id-to-MPIDR affinity is used only for TCG; KVM will 
> > override it.
> > -     * We don't support setting cluster ID ([16..23]) (known as Aff2
> > -     * in later ARM ARM versions), or any of the higher affinity level 
> > fields,
> > -     * so these bits always RAZ.
> > -     */
> > -    Aff1 = cs->cpu_index / ARM_CPUS_PER_CLUSTER;
> > -    Aff0 = cs->cpu_index % ARM_CPUS_PER_CLUSTER;
> > -    cpu->mp_affinity = (Aff1 << ARM_AFF1_SHIFT) | Aff0;
> > -
> >  #ifndef CONFIG_USER_ONLY
> >      /* Our inbound IRQ and FIQ lines */
> >      if (kvm_enabled()) {
> [...]
> > @@ -631,6 +628,15 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
> > **errp)
> >          set_feature(env, ARM_FEATURE_THUMB_DSP);
> >      }
> >  
> > +    /* This cpu-id-to-MPIDR affinity is used only for TCG; KVM will 
> > override it.
> > +     * We don't support setting cluster ID ([16..23]) (known as Aff2
> > +     * in later ARM ARM versions), or any of the higher affinity level 
> > fields,
> > +     * so these bits always RAZ.
> > +     */
> > +    Aff1 = cs->cpu_index / ARM_CPUS_PER_CLUSTER;
> > +    Aff0 = cs->cpu_index % ARM_CPUS_PER_CLUSTER;
> > +    cpu->mp_affinity = (Aff1 << ARM_AFF1_SHIFT) | Aff0;
> > +
> 
> This will override any value set in the "mp-affinity" property,
> The mp-affinity property can be set by the user in the
> command-line, and it is also set by machvirt_init() in
> hw/arm/virt.c.

I'm glad you noticed this Eduardo. We'd indeed lose changes made to
the MPIDRs for mach-virt and Raspberry Pi.

> 
> Considering that each CPU is supposed to have a different value,
> I doubt there are existing use cases for mp-affinity being set
> directly by the user.

Probably not. It was turned into a property in order for the gicv3
model to access it. I don't think that's necessary, so we can just
un-property it, accessing it directly from the structure instead.

> 
> I suggest having a "cluster-size" property, instead of
> "mp-affinity". This way the mp_affinity field can be calculated
> on realize, based on the configured cluster-size.

This won't work for Raspberry Pi's MPIDR adjustment. Anyway, IMO
realize should only set values when it knows nothing has been set.
If values have been set, it should only sanity check them. In this
case it's safe to simply check for uniqueness and zeros;

 1) The MPIDRs are all zero. As they're not all unique that's not
    valid. It's pretty safe to assume they just weren't set in this
    case though, so we can set the default values without complaining.
    If there was only one cpu, then MPIDR=0 is valid, but that's the
    default anyway.
 2) The MPIDRs are all unique, or there's a single cpu and its MPIDR
    is not zero. In this case we shouldn't touch them.
 3) The MPIDRs are not all zero and not all unique. This is a failed
    sanity check and should abort.

Thanks,
drew

> 
> >      if (cpu->reset_hivecs) {
> >              cpu->reset_sctlr |= (1 << 13);
> >      }
> [...]
> 
> -- 
> Eduardo
>