linux-kernel - Re: [EXTERNAL] Re: [PATCH v3] mm/thp: fix "mm: thp: kill __transhuge_page

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]

Date:   Fri, 25 Aug 2023 13:49:15 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Yang Shi <shy828301@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Saurabh Sengar <ssengar@...ux.microsoft.com>
Subject: Re: [EXTERNAL] Re: [PATCH v3] mm/thp: fix "mm: thp: kill
 __transhuge_page_enabled()"

On Fri, Aug 25, 2023 at 09:59:23AM +0200, David Hildenbrand wrote:
> Especially, we do have bigger ->huge_fault changes coming up:
> 
> https://lkml.kernel.org/r/20230818202335.2739663-1-willy@infradead.org
> 
> If the driver is not in the tree, people don't care.
> 
> You really should try upstreaming that driver.
> 
> 
> So this patch here adds complexity (which I don't like) in order to keep an
> OOT driver working -- possibly for a short time. I'm tempted to say "please
> fix your driver to not use huge faults in that scenario, it is no longer
> supported".
> 
> But I'm just about to vanish for 1.5 week into vacation :)
> 
> @Willy, what are your thoughts?

Fundamentally there was a bad assumption with the original patch --
it assumed that the only reason to support ->huge_fault was for DAX,
and that's not true.  It's just that the only drivers in-tree which
support ->huge_fault do so in order to support DAX.

Keeping a driver out of tree is always a risky and costly proposition.
It will continue to be broken by core kernel changes, particularly
if/when it does unusual things.

I think the complexity is entirely on us.  I think there's a simpler way
to handle the problem, but I'd start by turning all of this "admin and
app get to control when THP are used" nonsense into no-ops.