[PATCH -stable] arm64: mm: don't write garbage into TTBR1_EL1 register

[Jan Glauber]

On Mon, Feb 26, 2018 at 11:30:50AM +0000, Will Deacon wrote:
> Damnit, sorry again. I changed the argument order of phys_to_ttbr along
> the way, so must've confused myself during the backporting exercise. It's
> also one of those things that will lead to potential TLB corruption in rare
> circumstances where the junk in TTBR1 ends up giving a valid translation,
> so it didn't crop up in my testing. How did Nicolas see this? The bug
> report I saw didn't look related.

FWIW, we've been hitting this bug with a distribution backport on
ThunderX2 on every boot. Due to bad luck there was a non-zero value
in TTBR1 that crashed the kernel immediately and dropped us to firmware.

--Jan