From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f51.google.com (mail-pa0-f51.google.com [209.85.220.51]) by kanga.kvack.org (Postfix) with ESMTP id 8B5F46B0255 for ; Fri, 27 Nov 2015 04:32:59 -0500 (EST) Received: by padhx2 with SMTP id hx2so110371934pad.1 for ; Fri, 27 Nov 2015 01:32:59 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id v18si2343816pfi.251.2015.11.27.01.32.58 for ; Fri, 27 Nov 2015 01:32:58 -0800 (PST) Date: Fri, 27 Nov 2015 09:32:50 +0000 From: Catalin Marinas Subject: Re: [PATCH v3 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Message-ID: <20151127093249.GW3109@e104818-lin.cambridge.arm.com> References: <1447888808-31571-1-git-send-email-dcashman@android.com> <1447888808-31571-2-git-send-email-dcashman@android.com> <1447888808-31571-3-git-send-email-dcashman@android.com> <1447888808-31571-4-git-send-email-dcashman@android.com> <20151123150459.GD4236@arm.com> <56536114.1020305@android.com> <20151125120601.GC3109@e104818-lin.cambridge.arm.com> <56561C71.30602@android.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Ryabinin Cc: Daniel Cashman , "open list:DOCUMENTATION" , Will Deacon , "linux-mm@kvack.org" , "H. Peter Anvin" , mingo , aarcange@redhat.com, Russell King , "Kirill A. Shutemov" , Jonathan Corbet , xypron.glpk@gmx.de, "x86@kernel.org" , hecmargi@upv.es, Mel Gorman , David Rientjes , Borislav Petkov , nnk@google.com, dzickus@redhat.com, Kees Cook , jpoimboe@redhat.com, Thomas Gleixner , Andrew Morton , linux-arm-kernel@lists.infradead.org, LKML , salyzyn@android.com, "Eric W. Biederman" , jeffv@google.com, Naoya Horiguchi , dcashman@google.com On Fri, Nov 27, 2015 at 11:36:30AM +0300, Andrey Ryabinin wrote: > 2015-11-25 23:39 GMT+03:00 Daniel Cashman : > > On 11/25/2015 04:06 AM, Catalin Marinas wrote: > >> For KASan, we ended up calculating KASAN_SHADOW_OFFSET in > >> arch/arm64/Makefile. What would the formula be for the above > >> ARCH_MMAP_RND_BITS_MAX? > > > > The general formula I used ended up being: > > _max = floor(log(TASK_SIZE)) - log(PAGE_SIZE) - 3 > > For kasan, we calculate KASAN_SHADOW_OFFSET in Makefile, because we need to use > that value in Makefiles. > > For ARCH_MMAP_RND_COMPAT_BITS_MIN/MAX I don't see a reason why it has > to be in Kconfig. > Can't we just use your formula to #define ARCH_MMAP_RND_COMPAT_BITS_* > in some arch header? Because there is another option, ARCH_MMAP_RND_BITS depending on EXPERT which uses the MIN/MAX range defined per architecture. Since it's an expert feature, we could as well ignore the MIN/MAX in Kconfig and just add BUILD_BUG_ON checks to the code. This way we could simply define them in C files. Alternatively, add arithmetics support to kbuild ;). -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org