Re: [PATCH v3 7/9] xen/riscv: introduce and init SBI RFENCE extension

[oleksii.kurochko@xxxxxxxxx]

On Tue, 2024-07-30 at 11:17 +0200, Jan Beulich wrote:
> > > > +
> > > > +static void sbi_cpumask_to_hartmask(const struct cpumask
> > > > *cmask,
> > > > +                 struct cpumask *hmask)
> > > 
> > > I doubt it is valud to re-use struct cpumask for hart maps.
> > Why not? Would it be better to use unsigned long *hmask?
> 
> It's not only better, but imo a requirement. Unless there's a
> guarantee
> by the spec that hart IDs for any subset of harts are sequential and
> starting from 0, you just can't assume they fall in the [0,NR_CPUS)
> or
> really [0,nr_cpu_ids) range. Yet without that you simply can't
> (ab)use
> struct cpumask (and btw it wants to be cpumask_t everywhere).
> 
> You may want to take a look at struct physid_mask that we have on x86
> for the equivalent purpose.
Could you please explain me why factor 4 is used in defintion of
MAX_APICS and why 256 ( is it a maximum number of APIC IDs can be
supported in the system? ):
  #define MAX_APICS     MAX(256, 4 * NR_CPUS)

~ Oleksii