[PATCH 1/2] ARM: ioremap: Flush PGDs for VMALLOC shadow

[Ard Biesheuvel]

On Wed, 16 Oct 2024 at 20:38, Linus Walleij <linus.walleij at linaro.org> wrote:
>
> On Wed, Oct 16, 2024 at 1:33 PM Ard Biesheuvel <ardb at kernel.org> wrote:
>
> > > @@ -125,6 +126,12 @@ void __check_vmalloc_seq(struct mm_struct *mm)
> (...)
> > Then, there is another part to this: in arch/arm/kernel/traps.c, we
> > have the following code
> >
> > void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
> > {
> >     if (start < VMALLOC_END && end > VMALLOC_START)
> >         atomic_inc_return_release(&init_mm.context.vmalloc_seq);
> > }
> >
> > where we only bump vmalloc_seq if the updated region overlaps with the
> > vmalloc region, so this will need a similar treatment afaict.
>
> Not really, right? We bump init_mm.context.vmalloc_seq if the address
> overlaps the entire vmalloc area.
>
> Then the previously patched __check_vmalloc_seq() will check that
> atomic counter and copy the PGD entries, and with the code in this
> patch it will also copy (sync) the corresponding shadow memory
> at that point.
>

Yes, so we rely on the fact that changes to the vmalloc area and
changes to the associated shadow mappings always occur in combination,
right?

I think that should probably be safe, but we have to be sure.