[PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64

[Marco Elver]

On Mon, 21 Sep 2020 at 19:44, Will Deacon <will at kernel.org> wrote:
[...]
> > > > > For ARM64, we would like to solicit feedback on what the best option is
> > > > > to obtain a constant address for __kfence_pool. One option is to declare
> > > > > a memory range in the memory layout to be dedicated to KFENCE (like is
> > > > > done for KASAN), however, it is unclear if this is the best available
> > > > > option. We would like to avoid touching the memory layout.
> > > >
> > > > Sorry for the delay on this.
> > >
> > > NP, thanks for looking!
> > >
> > > > Given that the pool is relatively small (i.e. when compared with our virtual
> > > > address space), dedicating an area of virtual space sounds like it makes
> > > > the most sense here. How early do you need it to be available?
> > >
> > > Yes, having a dedicated address sounds good.
> > > We're inserting kfence_init() into start_kernel() after timekeeping_init().
> > > So way after mm_init(), if that matters.
> >
> > The question is though, how big should that dedicated area be?
> > Right now KFENCE_NUM_OBJECTS can be up to 16383 (which makes the pool
> > size 64MB), but this number actually comes from the limitation on
> > static objects, so we might want to increase that number on arm64.
>
> What happens on x86 and why would we do something different?

On x86 we just do `char __kfence_pool[KFENCE_POOL_SIZE] ...;` to
statically allocate the pool. On arm64 this doesn't seem to work
because static memory doesn't have struct pages?

Thanks,
-- Marco