Re: [PATCH v1 07/24] kvm: arm64: Create nVHE copy of cpu_logical_map

[Marc Zyngier]

On 2020-11-11 13:03, David Brazdil wrote:
> > > +/*
> > > + * nVHE copy of data structures tracking available CPU cores.
> > > + * Only entries for CPUs that were online at KVM init are populated.
> > > + * Other CPUs should not be allowed to boot because their features were
> > > + * not checked against the finalized system capabilities.
> > > + */
> > > +u64 __ro_after_init __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1]
> > > = INVALID_HWID };
> >
> > I'm not sure what __ro_after_init means once we get S2 isolation.
>
> It is stretching the definition of 'init' a bit, I know, but I don't 
> see what
> your worry is about S2? The intention is to mark this read-only for 
> .hyp.text
> at runtime. With S2, the host won't be able to write to it after KVM 
> init.
> Obviously that's currently not the case.

More importantly, EL2 can write to it at any time, which is the bit I'm 
worried
about, as it makes the annotation misleading.

> One thing we might change in the future is marking it RW for some 
> initial
> setup in a HVC handler, then marking it RO for the rest of uptime.

That'd be a desirable outcome, and it would be consistent with the rest
of the kernel.

> > > +
> > > +u64 cpu_logical_map(int cpu)
> >
> > nit: is there any reason why "cpu" cannot be unsigned? The thought
> > of a negative CPU number makes me shiver...
>
> Same here. That's how it's defined in kernel proper, so I went with 
> that.

I'm happy to deviate from the kernel (give the function a different name
if this clashes with existing include files).

We can also fix the rest of the kernel (I've just written the trivial 
patch).

> > > +{
> > > +	if (cpu < 0 || cpu >= ARRAY_SIZE(__cpu_logical_map))
> > > +		hyp_panic();
> > > +
> > > +	return __cpu_logical_map[cpu];
> > > +}
> > > +
> > >  unsigned long __hyp_per_cpu_offset(unsigned int cpu)
> > >  {
> > >  	unsigned long *cpu_base_array;
> >
> > Overall, this patch would make more sense closer it its use case
> > (in patch 19). I also don't understand why this lives in percpu.c...
>
> I didn't think it called for adding another C file for this. How about 
> we
> rename this file to smp.c? Would that make sense for both?

Make that hyp-smp.c, please!

        M.
--
Jazz is not dead. It just smells funny...