Re: [PATCH v1 06/24] kvm: arm64: Support per_cpu_ptr in nVHE hyp code

[Marc Zyngier]

On 2020-11-11 12:32, David Brazdil wrote:
> > > +
> > > +	cpu_base_array = kern_hyp_va(&kvm_arm_hyp_percpu_base[0]);
> >
> > There is no guarantee that this will not generate a PC relative
> > addressing, resulting in kern_hyp_va() being applied twice.
> >
> > Consider using hyp_symbol_addr() instead, which always does the right
> > by forcing a PC relative addressing and not subsequently mangling
> > the address.
> >
> > > +	this_cpu_base = kern_hyp_va(cpu_base_array[cpu]);
> > > +	return this_cpu_base - (unsigned long)&__per_cpu_start;
> >
> > And this is the opposite case: if the compiler generates an absolute
> > address, you're toast. Yes, this is just as unlikely, but hey...
> > Same remedy should apply.
>
> Good point, and I'll probably keep forgetting about this in the future. 
> Now
> that all .hyp.text is only executed under hyp page tables, should we 
> start
> thinking about fixing up the relocations?

Why not, if you can deal with the hypervisor text being mapped at a 
random
location, and make sure that the kernel doesn't process the relocations
for you. This would certainly save us a lot of runtime offsetting (which
I'm adding to in a separate series).

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