From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f50.google.com (mail-pa0-f50.google.com [209.85.220.50]) by kanga.kvack.org (Postfix) with ESMTP id 38C186B0257 for ; Thu, 3 Dec 2015 11:12:41 -0500 (EST) Received: by pacej9 with SMTP id ej9so71366976pac.2 for ; Thu, 03 Dec 2015 08:12:41 -0800 (PST) Received: from mail-pa0-x22d.google.com (mail-pa0-x22d.google.com. [2607:f8b0:400e:c03::22d]) by mx.google.com with ESMTPS id d1si12781228pas.96.2015.12.03.08.12.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Dec 2015 08:12:40 -0800 (PST) Received: by pabfh17 with SMTP id fh17so73336228pab.0 for ; Thu, 03 Dec 2015 08:12:40 -0800 (PST) Subject: Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. References: <1449000658-11475-1-git-send-email-dcashman@android.com> <1449000658-11475-2-git-send-email-dcashman@android.com> <1449000658-11475-3-git-send-email-dcashman@android.com> <1449000658-11475-4-git-send-email-dcashman@android.com> <20151203121712.GE11337@arm.com> From: Daniel Cashman Message-ID: <566069F0.3060409@android.com> Date: Thu, 3 Dec 2015 08:12:32 -0800 MIME-Version: 1.0 In-Reply-To: <20151203121712.GE11337@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Will Deacon Cc: linux-kernel@vger.kernel.org, linux@arm.linux.org.uk, akpm@linux-foundation.org, keescook@chromium.org, mingo@kernel.org, linux-arm-kernel@lists.infradead.org, corbet@lwn.net, dzickus@redhat.com, ebiederm@xmission.com, xypron.glpk@gmx.de, jpoimboe@redhat.com, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, mgorman@suse.de, tglx@linutronix.de, rientjes@google.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, salyzyn@android.com, jeffv@google.com, nnk@google.com, catalin.marinas@arm.com, hpa@zytor.com, x86@kernel.org, hecmargi@upv.es, bp@suse.de, dcashman@google.com, arnd@arndb.de On 12/3/15 4:17 AM, Will Deacon wrote: >> + select HAVE_ARCH_MMAP_RND_BITS if MMU >> + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT > > You can drop the 'if MMU' bits, since we don't support !MMU on arm64. Ok, will do. I was a little uneasy leaving it implicit, but even if something w/out MMU on arm64 shows up, it'll easily be corrected. >> +config ARCH_MMAP_RND_BITS_MIN >> + default 15 if ARM64_64K_PAGES >> + default 17 if ARM64_16K_PAGES >> + default 19 > > Is this correct? We currently have a mask of 0x3ffff, so that's 18 bits. Off-by-one errors provide a good example of why hardening features are useful? =/ Will change. >> +config ARCH_MMAP_RND_BITS_MAX >> + default 19 if ARM64_VA_BITS=36 >> + default 20 if ARM64_64K_PAGES && ARM64_VA_BITS=39 >> + default 22 if ARM64_16K_PAGES && ARM64_VA_BITS=39 >> + default 24 if ARM64_VA_BITS=39 >> + default 23 if ARM64_64K_PAGES && ARM64_VA_BITS=42 >> + default 25 if ARM64_16K_PAGES && ARM64_VA_BITS=42 >> + default 27 if ARM64_VA_BITS=42 >> + default 30 if ARM64_VA_BITS=47 >> + default 29 if ARM64_64K_PAGES && ARM64_VA_BITS=48 >> + default 31 if ARM64_16K_PAGES && ARM64_VA_BITS=48 >> + default 33 if ARM64_VA_BITS=48 >> + default 15 if ARM64_64K_PAGES >> + default 17 if ARM64_16K_PAGES >> + default 19 > > Could you add a comment above this with the formula > (VA_BITS - PAGE_SHIFT - 3), please, so that we can update this easily in > the future if we need to? > Yes, seems reasonable. Time will tell if this remains true for all architectures, or even here, but it would be good to document it where someone considering a change could easily find it. Thank You, Dan -- 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