linux-kernel - Re: [patch V4 2/8] mm/highmem: Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE

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Date:   Thu, 19 Nov 2020 08:46:01 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [patch V4 2/8] mm/highmem: Provide
 CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP

On Wed, Nov 18, 2020 at 01:13:57PM -0800, Linus Torvalds wrote:
> On Wed, Nov 18, 2020 at 12:58 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP which forces the temporary
> > mapping even for lowmem pages. This needs to be a seperate config switch
> > because this only works on architectures which do not have cache aliasing
> > problems.
> 
> Very good. And you made sure to have a comment to not enable it for
> production systems.
> 
> Hopefully people will even read it ;)
> 

And not start thinking it as a security hardening option.

-- 
Mel Gorman
SUSE Labs