linux-kernel - Re: [PATCH] mm: fix finish_fault() handling for large folios

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CADyq12x8eJ8ASq6WOEkFFbmJYajLnPd+qM8+QP1W76Add=S67A@mail.gmail.com>
Date: Wed, 26 Feb 2025 09:31:51 -0500
From: Brian Geffon <bgeffon@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Zi Yan <ziy@...dia.com>, 
	Kefeng Wang <wangkefeng.wang@...wei.com>, Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, Hugh Dickins <hughd@...gle.com>, 
	Marek Maslanka <mmaslanka@...gle.com>
Subject: Re: [PATCH] mm: fix finish_fault() handling for large folios

On Wed, Feb 26, 2025 at 9:04 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Feb 26, 2025 at 06:48:15AM -0500, Brian Geffon wrote:
> > When handling faults for anon shmem finish_fault() will attempt to install
> > ptes for the entire folio. Unfortunately if it encounters a single
> > non-pte_none entry in that range it will bail, even if the pte that
> > triggered the fault is still pte_none. When this situation happens the
> > fault will be retried endlessly never making forward progress.
> >
> > This patch fixes this behavior and if it detects that a pte in the range
> > is not pte_none it will fall back to setting just the pte for the
> > address that triggered the fault.
>
> Surely there's a similar problem in do_anonymous_page()?
>
> At any rate, what a horrid function finish_fault() has become.
> Special cases all over the place.  What we should be doing is
> deciding the range of PTEs to insert, bounded by the folio, the VMA
> and any non-none entries.  Maybe I'll get a chance to fix this up.

I agree, I wasn't thrilled that the fix looked like this but I was
trying to keep the change minimal to aid in backporting to stable
kernels where this behavior is broken. With that being said, do you
have a preference on a minimal way we can fix this before
finish_fault() gets a proper cleanup?