[PATCH v3] arm64: mm: move zero page from .bss to right before swapper_pg_dir

[Ard Biesheuvel]

On 13 September 2016 at 21:24, Mark Rutland <mark.rutland at arm.com> wrote:
> On Tue, Sep 13, 2016 at 08:18:52PM +0100, Ard Biesheuvel wrote:
>> On 13 September 2016 at 18:35, Mark Rutland <mark.rutland at arm.com> wrote:
>> Thanks. But actually, I think it makes sense to make the first
>> swapper_pg_dir page read-only as well, given that it is only modified
>> via the fixmap, and we can trivially extend the r/o bss region to end
>> at 'swapper_pg_dir + PAGE_SIZE'
>>
>> Thoughts?
>
> I thought that we lazy-allocated the vmalloc region at runtime, and initialised
> pgd level entries.
>
> From a quick dig it looks like a vmalloc() could eventually call
> pgd_populate(), which seems to set a pgd entry without using a fixmap slot.
>
> Is there some reason that won't happen at runtime?
>

Ah, right. I thought all swapper_pg_dir manipulations went via the
arch64/mm/mmu.c routines that use the fixmap slots, but apparently
this is not the case.