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[209.85.208.181]) by smtp.gmail.com with ESMTPSA id w22sm16379ljm.20.2020.11.19.09.20.02 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Nov 2020 09:20:03 -0800 (PST) Received: by mail-lj1-f181.google.com with SMTP id b17so7029813ljf.12 for ; Thu, 19 Nov 2020 09:20:02 -0800 (PST) X-Received: by 2002:a2e:8e33:: with SMTP id r19mr5940506ljk.102.1605806402308; Thu, 19 Nov 2020 09:20:02 -0800 (PST) MIME-Version: 1.0 References: <20201118194838.753436396@linutronix.de> <20201118204007.028261233@linutronix.de> <20201119084601.GG3306@suse.de> In-Reply-To: <20201119084601.GG3306@suse.de> From: Linus Torvalds Date: Thu, 19 Nov 2020 09:19:46 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch V4 2/8] mm/highmem: Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP To: Mel Gorman Cc: Thomas Gleixner , LKML , "the arch/x86 maintainers" , Christoph Hellwig , Matthew Wilcox , Daniel Vetter , Andrew Morton , Linux-MM , Peter Zijlstra , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira 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 Thu, Nov 19, 2020 at 12:46 AM Mel Gorman wrote: > > And not start thinking it as a security hardening option. It's probably the reverse of a hardening option, since it will cause mapping of stuff in known and controllable virtual addresses. Although any kmap'able page is likely to already be something you can read anyway (ie page cache long after security checks have been done). So it probably really doesn't matter either way. The only thing that is certain is that it's going to slow down important code-paths. Linus