Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752724AbbKYUjU (ORCPT ); Wed, 25 Nov 2015 15:39:20 -0500 Received: from mail-pa0-f53.google.com ([209.85.220.53]:33000 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751327AbbKYUjQ (ORCPT ); Wed, 25 Nov 2015 15:39:16 -0500 Subject: Re: [PATCH v3 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. To: Catalin Marinas 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> Cc: Will Deacon , dcashman@google.com, linux-doc@vger.kernel.org, linux-mm@kvack.org, hpa@zytor.com, mingo@kernel.org, aarcange@redhat.com, linux@arm.linux.org.uk, corbet@lwn.net, xypron.glpk@gmx.de, x86@kernel.org, hecmargi@upv.es, mgorman@suse.de, rientjes@google.com, bp@suse.de, nnk@google.com, dzickus@redhat.com, keescook@chromium.org, jpoimboe@redhat.com, tglx@linutronix.de, n-horiguchi@ah.jp.nec.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, salyzyn@android.com, ebiederm@xmission.com, jeffv@google.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com From: Daniel Cashman Message-ID: <56561C71.30602@android.com> Date: Wed, 25 Nov 2015 12:39:13 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151125120601.GC3109@e104818-lin.cambridge.arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2342 Lines: 58 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 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/