Re: [PATCH v1 05/15] xen/riscv: implement stub for smp_send_event_check_mask()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 1/12/26 6:05 PM, Jan Beulich wrote:
> On 12.01.2026 17:53, Oleksii Kurochko wrote:
> > On 1/7/26 4:47 PM, Jan Beulich wrote:
> > > On 24.12.2025 18:03, Oleksii Kurochko wrote:
> > > > @@ -13,3 +14,10 @@
> > > >    struct pcpu_info pcpu_info[NR_CPUS] = { [0 ... NR_CPUS - 1] = {
> > > >        .processor_id = NR_CPUS,
> > > >    }};
> > > > +
> > > > +void smp_send_event_check_mask(const cpumask_t *mask)
> > > > +{
> > > > +#if CONFIG_NR_CPUS > 1
> > > > +# error "smp_send_event_check_mask() unimplemented"
> > > > +#endif
> > > > +}
> > > CONFIG_NR_CPUS is 64 by default for 64-bit arch-es, from all I can tell, also
> > > for RISC-V. And there's no "override" in riscv64_defconfig. How is the above
> > > going to work in CI? Then again I must be overlooking something, as the config
> > > used in CI has CONFIG_NR_CPUS=1. Just that I can't tell why that is.
> > It is 1 because of the defintion of NR_CPUS in KConfig:
> > config NR_CPUS
> >         int "Maximum number of CPUs"
> >         range 1 1 if ARM && MPU
> >         range 1 16383
> >           .... ( all other range props are condtional and there is no RISC-V in 
> > dependency)
> > so for RISC-V "range 1 16383" used and CONFIG_NR_CPUS is set to the minimal of 
> > this range,
> > so it is 1.
> I fear I don't follow: Why would the lowest value be picked, rather than the
> specified default (which would be 64 for RV64)? That's what I thought the
> default values are there (among other purposes).
But there is no default for RISC-V for config NR_CPUS:

  config NR_CPUS
          int "Maximum number of CPUs"
          range 1 1 if ARM && MPU
          range 1 16383
          default "256" if X86
          default "1" if ARM && MPU
          default "8" if ARM && RCAR3
          default "4" if ARM && QEMU
          default "4" if ARM && MPSOC
          default "128" if ARM
          help
            ...

So a value from range [1, 16383] is chosen and based on the code of 
sym_validate_range():
        ...
        val = strtoll(sym->curr.val, NULL, base);
        val2 = sym_get_range_val(prop->expr->left.sym, base);
        if (val >= val2) {
                val2 = sym_get_range_val(prop->expr->right.sym, base);
                if (val <= val2)
                        return;
        }
        if (sym->type == S_INT)
                sprintf(str, "%lld", val2);
        else
                sprintf(str, "0x%llx", val2);
        sym->curr.val = xstrdup(str);

First initialization of val2 it is the left value of the range [1, 16383],so it 
is 1
and val is 0 (I assume so that it is by initialization 0), thereby val2 = 1 
will be
used as a value for NR_CPUS.

I also experimented by trying to update it to the range|2 16383|, 
and|CONFIG_NR_CPUS|
became 2.

~ Oleksii