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: <Y8a9+ywh65fmuKvv@dhcp22.suse.cz>
Date:   Tue, 17 Jan 2023 16:25:47 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, michel@...pinasse.org,
        jglisse@...gle.com, vbabka@...e.cz, hannes@...xchg.org,
        mgorman@...hsingularity.net, dave@...olabs.net,
        willy@...radead.org, liam.howlett@...cle.com, peterz@...radead.org,
        ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
        paulmck@...nel.org, luto@...nel.org, songliubraving@...com,
        peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        punit.agrawal@...edance.com, lstoakes@...il.com,
        peterjung1337@...il.com, rientjes@...gle.com,
        axelrasmussen@...gle.com, joelaf@...gle.com, minchan@...gle.com,
        jannh@...gle.com, shakeelb@...gle.com, tatashin@...gle.com,
        edumazet@...gle.com, gthelen@...gle.com, gurua@...gle.com,
        arjunroy@...gle.com, soheil@...gle.com, hughlynch@...gle.com,
        leewalsh@...gle.com, posk@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 18/41] mm/khugepaged: write-lock VMA while collapsing a
 huge page

On Mon 09-01-23 12:53:13, Suren Baghdasaryan wrote:
> Protect VMA from concurrent page fault handler while collapsing a huge
> page. Page fault handler needs a stable PMD to use PTL and relies on
> per-VMA lock to prevent concurrent PMD changes. pmdp_collapse_flush(),
> set_huge_pmd() and collapse_and_free_pmd() can modify a PMD, which will
> not be detected by a page fault handler without proper locking.

I am struggling with this changelog. Maybe because my recollection of
the THP collapsing subtleties is weak. But aren't you just trying to say
that the current #PF handling and THP collapsing need to be mutually
exclusive currently so in order to keep that assumption you have mark
the vma write locked?

Also it is not really clear to me how that handles other vmas which can
share the same thp?
-- 
Michal Hocko
SUSE Labs

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ