From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Fri, 27 Nov 2015 09:32:50 +0000 Subject: [PATCH v3 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. In-Reply-To: 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> Message-ID: <20151127093249.GW3109@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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