Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754117AbbK0Igf (ORCPT ); Fri, 27 Nov 2015 03:36:35 -0500 Received: from mail-wm0-f51.google.com ([74.125.82.51]:34838 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751504AbbK0Igc (ORCPT ); Fri, 27 Nov 2015 03:36:32 -0500 MIME-Version: 1.0 In-Reply-To: <56561C71.30602@android.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> Date: Fri, 27 Nov 2015 11:36:30 +0300 Message-ID: Subject: Re: [PATCH v3 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. From: Andrey Ryabinin To: Daniel Cashman Cc: Catalin Marinas , Will Deacon , dcashman@google.com, "open list:DOCUMENTATION" , "linux-mm@kvack.org" , "H. Peter Anvin" , mingo , aarcange@redhat.com, Russell King , 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 , Naoya Horiguchi , linux-arm-kernel@lists.infradead.org, LKML , salyzyn@android.com, "Eric W. Biederman" , jeffv@google.com, Andrew Morton , "Kirill A. Shutemov" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2759 Lines: 69 2015-11-25 23:39 GMT+03:00 Daniel Cashman : > On 11/25/2015 04:06 AM, Catalin Marinas wrote: >> On Mon, Nov 23, 2015 at 10:55:16AM -0800, Daniel Cashman wrote: >>> On 11/23/2015 07:04 AM, Will Deacon wrote: >>>> On Wed, Nov 18, 2015 at 03:20:07PM -0800, Daniel Cashman wrote: >>>>> +config ARCH_MMAP_RND_BITS_MAX >>>>> + default 20 if ARM64_64K_PAGES && ARCH_VA_BITS=39 >> >> Where is ARCH_VA_BITS defined? We only have options like >> ARM64_VA_BITS_39. >> >> BTW, we no longer allow the 64K pages and 39-bit VA combination. > > It is not, and should have been ARM64_VA_BITS. This stanza was meant to > mimic the one for ARM64_VA_BITS. Thank you for pointing this, and the > 39-bit combination out. > >>>>> + default 24 if ARCH_VA_BITS=39 >>>>> + default 23 if ARM64_64K_PAGES && ARCH_VA_BITS=42 >>>>> + default 27 if ARCH_VA_BITS=42 >>>>> + default 29 if ARM64_64K_PAGES && ARCH_VA_BITS=48 >>>>> + default 33 if ARCH_VA_BITS=48 >>>>> + default 15 if ARM64_64K_PAGES >>>>> + default 19 >>>>> + >>>>> +config ARCH_MMAP_RND_COMPAT_BITS_MIN >>>>> + default 7 if ARM64_64K_PAGES >>>>> + default 11 >>>> >>>> FYI: we now support 16k pages too, so this might need updating. It would >>>> be much nicer if this was somehow computed rather than have the results >>>> all open-coded like this. >>> >>> Yes, I ideally wanted this to be calculated based on the different page >>> options and VA_BITS (which itself has a similar stanza), but I don't >>> know how to do that/if it is currently supported in Kconfig. This would >>> be even more desirable with the addition of 16K_PAGES, as with this >>> setup we have a combinatorial problem. >> >> 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? > which in the case of arm64 ended up being VA_BITS - PAGE_SHIFT - 3. > Aside: following this would actually put COMPAT_BITS_MAX at 17 for 4k > pages, rather than 16, but I left it at 16 to mirror what was put in > arch/arm/Kconfig. > > > Thank You, > Dan > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/