Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sat, 26 Dec 2020 16:45:55 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Will Deacon <will@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vinayak Menon <vinmenon@codeaurora.org>,
        Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries
 when prefaulting
In-Reply-To: <20201226224016.dxjmordcfj75xgte@box>
Message-ID: <alpine.LSU.2.11.2012261623140.1022@eggly.anvils>
References: <CAHk-=wgO2LsoKhX7MjSECo+Xrj1-Me7tzRfNcsdEZBRwJW1cQg@mail.gmail.com> <20201219124103.w6isern3ywc7xbur@box> <CAHk-=wifcVaxaTn_RbZ=idfYFazTPwm8t5cB1rY6xEBjbcfO5g@mail.gmail.com> <20201222100047.p5zdb4ghagncq2oe@box> <alpine.LSU.2.11.2012231905300.5723@eggly.anvils>
 <20201225113157.e7hmluffh56fszfc@box> <CAHk-=wiT50aEErZgZOrbFQ=GhFuM3MnBmHoSBSScN9rmXMnOKQ@mail.gmail.com> <20201226204335.dikqkrkezqet6oqf@box> <alpine.LSU.2.11.2012261246450.1629@eggly.anvils> <CAHk-=wjesveWEQZ4tqRssSSQvuxx46LqYfME+uxKfghxAe6U_w@mail.gmail.com>
 <20201226224016.dxjmordcfj75xgte@box>
User-Agent: Alpine 2.11 (LSU 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk

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