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

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Date:   Sat, 26 Dec 2020 16:45:55 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jan Kara <jack@...e.cz>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries
 when prefaulting

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