[PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting

[Hugh Dickins]

On Sun, 27 Dec 2020, Kirill A. Shutemov wrote:
> 
> Here's the fixup I have so far. It doesn't blow up immediately, but please
> take a closer look. Who knows what stupid mistake I did this time. :/

It's been running fine on x86_64 for a couple of hours (but of course
my testing is deficient, in not detecting the case Linus spotted).

But I just thought I'd try it on i386 (hadn't tried previous versions)
and this has a new disappointment: crashes when booting, in the "check
if the page fault is solved" in do_fault_around().  I imagine a highmem
issue with kmap of the pte address, but I'm reporting now before looking
into it further (but verified that current linux.git i386 boots up fine).

Maybe easily fixed: but does suggest this needs exposure in linux-next.

Hugh