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

[Marc Zyngier]

On 2020-11-11 13:45, David Brazdil wrote:
> On Wed, Nov 11, 2020 at 01:29:29PM +0000, Marc Zyngier wrote:
> > 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.
>
> EL2 can't, at least not accidentally. The hyp memory mapping is 
> PAGE_HYP_RO
> (see patch 05).

Ah, I obviously overlooked that. Thanks for setting me straight.

> Shouldn't clash with include files. Where fixing the kernel might clash 
> is
> all the users of for_each_*_cpu that use an int for the iterator var.

I don't think that's a problem (nobody expects that many CPUs). But if 
you
are confident that we don't have a problem, no need to change the kernel
itself.

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