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

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Date:   Mon, 28 Dec 2020 15:28:23 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     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 Mon, Dec 28, 2020 at 2:05 PM Kirill A. Shutemov <kirill@...temov.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