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[209.85.208.172]) by smtp.gmail.com with ESMTPSA id t15sm1394987ljg.139.2020.09.19.12.19.16 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 19 Sep 2020 12:19:16 -0700 (PDT) Received: by mail-lj1-f172.google.com with SMTP id k25so7760378ljg.9 for ; Sat, 19 Sep 2020 12:19:16 -0700 (PDT) X-Received: by 2002:a19:8907:: with SMTP id l7mr12464193lfd.105.1600542797553; Sat, 19 Sep 2020 12:13:17 -0700 (PDT) MIME-Version: 1.0 References: <20200919091751.011116649@linutronix.de> <20200919173906.GQ32101@casper.infradead.org> In-Reply-To: <20200919173906.GQ32101@casper.infradead.org> From: Linus Torvalds Date: Sat, 19 Sep 2020 12:13:01 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends To: Matthew Wilcox Cc: Thomas Gleixner , LKML , linux-arch , Paul McKenney , "the arch/x86 maintainers" , Sebastian Andrzej Siewior , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Andrew Morton , Linux-MM , Russell King , Linux ARM , Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , intel-gfx , dri-devel , Ard Biesheuvel , Herbert Xu , Vineet Gupta , "open list:SYNOPSYS ARC ARCHITECTURE" , Arnd Bergmann , Guo Ren , linux-csky@vger.kernel.org, Michal Simek , Thomas Bogendoerfer , linux-mips@vger.kernel.org, Nick Hu , Greentime Hu , Vincent Chen , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev , "David S. Miller" , linux-sparc Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Sep 19, 2020 at 10:39 AM Matthew Wilcox wrote: > > My concern with that is people might use kmap() and then pass the address > to a different task. So we need to audit the current users of kmap() > and convert any that do that into using vmap() instead. Ahh. Yes, I guess they might do that. It sounds strange, but not entirely crazy - I could imagine some "PIO thread" that does IO to a page that has been set up by somebody else using kmap(). Or similar. Linus