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

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: <alpine.LSU.2.11.2012261816520.1071@eggly.anvils>
Date:   Sat, 26 Dec 2020 18:38:32 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        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 Sat, 26 Dec 2020, Hugh Dickins wrote:
> 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).

This patch (like its antecedents) moves the pte_unmap_unlock() from
after do_fault_around()'s "check if the page fault is solved" into
filemap_map_pages() itself (which apparently does not NULLify vmf->pte
after unmapping it, which is poor, but good for revealing this issue).
That looks cleaner, but of course there was a very good reason for its
original positioning.

Maybe you want to change the ->map_pages prototype, to pass down the
requested address too, so that it can report whether the requested
address was resolved or not.  Or it could be left to __do_fault(),
or even to a repeated fault; but those would be less efficient.

> 
> Maybe easily fixed: but does suggest this needs exposure in linux-next.
> 
> Hugh