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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 28 Dec 2020 15:28:23 -0800
Message-ID: <CAHk-=wjquk=AxcbqA0UapYsHipa+myB4ayhttm6-Rb1Q5prKMw@mail.gmail.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     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>
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On Mon, Dec 28, 2020 at 2:05 PM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
>
> But I *think* we should be fine here: do_fault_around() limits start_pgoff
> and end_pgoff to stay within the page table.

Yeah, but I was thinking it would then update ->pte to just past the edge.

But looking at that logic, you're right - it will update ->pte and
->address only just before installing the pte, so it will never go
_to_ the edge, it will always stay inside.

So scratch my suspicion. It looked promising mainly because that ->pte
pointer update was one of the things that changed when you instead
compared against the address.

         Linus