[PATCH 4/5 v10] ARM: Initialize the mapping of KASan shadow memory

[Linus Walleij]

Hi Mike!

First a BIG THANKS for your help! With the aid of your review comments
and the further comments from Russell I have really progressed with this
patch set the last few days.

On Mon, Jun 15, 2020 at 4:33 PM Mike Rapoport <rppt at linux.ibm.com> wrote:

> > -#define pud_populate(mm,pmd,pte)     BUG()
> > -
> > +#ifndef CONFIG_KASAN
> > +#define pud_populate(mm, pmd, pte)   BUG()
> > +#else
> > +#define pud_populate(mm, pmd, pte)   do { } while (0)
>
> Hmm, is this really necessary? Regardless of CONFIG_KASAN pud_populate()
> should never be called for non-LPAE case...

It is necessary because the generic KASan code in
mm/kasan/init.c unconditionally calls pud_populate() and act as
if pud's always exist and need to be populated.

Possibly this means that pud_populate() should just be turned
into do { } while (0) as well (like other functions called unconditionally
from the VMM) but I'll leave this in for now.

>         cpu_switch_mm(tmp_pgd_table, &init_mm);
>
> And, why do we need a context switch here at all?

This is really just a way of reusing that function call to replace
the master page table pointer TTBR0 (Translation Table Base Register)
while setting up the shadow memory.

Yours,
Linus Walleij