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

[Mark Rutland]

On Fri, Sep 25, 2020 at 05:25:11PM +0200, Alexander Potapenko wrote:
> Will,
> 
> > 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?
> 
> How do we assign struct pages to a fixed virtual space area (I'm
> currently experimenting with 0xffff7f0000000000-0xffff7f0000200000)?

You don't.

There should be a struct page for each of the /physical/ pages, and
these can be found:

* via the physical address, using phyts_to_page() or pfn_to_page()
* via the linear/direct map, using virt_to_page()
* via the vmalloc page tables using vmalloc_to_page()

If you need virt_to_page() to work, the address has to be part of the
linear/direct map.

If you need to find the struct page for something that's part of the
kernel image you can use virt_to_page(lm_alias(x)).

> Looks like filling page table entries (similarly to what's being done
> in arch/arm64/mm/kasan_init.c) is not enough.
> I thought maybe vmemmap_populate() would do the job, but it didn't
> (virt_to_pfn() still returns invalid PFNs).

As above, I think lm_alias() will solve the problem here. Please see
that and CONFIG_DEBUG_VIRTUAL.

Thanks,
Mark.