From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67B05C433EF for ; Mon, 14 Feb 2022 21:07:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BEDED6B0075; Mon, 14 Feb 2022 16:07:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B77266B007B; Mon, 14 Feb 2022 16:07:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A16EC6B007D; Mon, 14 Feb 2022 16:07:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0084.hostedemail.com [216.40.44.84]) by kanga.kvack.org (Postfix) with ESMTP id 8E95A6B0075 for ; Mon, 14 Feb 2022 16:07:13 -0500 (EST) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 41D03180AC321 for ; Mon, 14 Feb 2022 21:07:13 +0000 (UTC) X-FDA: 79142620746.26.3E05785 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf01.hostedemail.com (Postfix) with ESMTP id 9C5DA40008 for ; Mon, 14 Feb 2022 21:07:12 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id ABB93139F; Mon, 14 Feb 2022 13:07:11 -0800 (PST) Received: from [10.57.70.89] (unknown [10.57.70.89]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A689F3F718; Mon, 14 Feb 2022 13:07:04 -0800 (PST) Message-ID: Date: Mon, 14 Feb 2022 21:06:58 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: [PATCH 08/14] arm64: simplify access_ok() Content-Language: en-GB To: Arnd Bergmann , Linus Torvalds , Christoph Hellwig , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, arnd@arndb.de, linux-kernel@vger.kernel.org Cc: linux@armlinux.org.uk, will@kernel.org, guoren@kernel.org, bcain@codeaurora.org, geert@linux-m68k.org, monstr@monstr.eu, tsbogend@alpha.franken.de, nickhu@andestech.com, green.hu@gmail.com, dinguyen@kernel.org, shorne@gmail.com, deller@gmx.de, mpe@ellerman.id.au, peterz@infradead.org, mingo@redhat.com, mark.rutland@arm.com, hca@linux.ibm.com, dalias@libc.org, davem@davemloft.net, richard@nod.at, x86@kernel.org, jcmvbkbc@gmail.com, ebiederm@xmission.com, akpm@linux-foundation.org, ardb@kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org References: <20220214163452.1568807-1-arnd@kernel.org> <20220214163452.1568807-9-arnd@kernel.org> From: Robin Murphy In-Reply-To: <20220214163452.1568807-9-arnd@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Authentication-Results: imf01.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf01.hostedemail.com: domain of robin.murphy@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=robin.murphy@arm.com X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9C5DA40008 X-Stat-Signature: s6qyukb98zhs8n4f3cuama5hudagqho7 X-HE-Tag: 1644872832-846131 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022-02-14 16:34, Arnd Bergmann wrote: > From: Arnd Bergmann > > arm64 has an inline asm implementation of access_ok() that is derived from > the 32-bit arm version and optimized for the case that both the limit and > the size are variable. With set_fs() gone, the limit is always constant, > and the size usually is as well, so just using the default implementation > reduces the check into a comparison against a constant that can be > scheduled by the compiler. Aww, I still vividly remember the birth of this madness, sat with my phone on a Saturday morning waiting for my bike to be MOT'd, staring at the 7-instruction sequence that Mark and I had come up with and certain that it could be shortened still. Kinda sad to see it go, but at the same time, glad that it can. Acked-by: Robin Murphy > On a defconfig build, this saves over 28KB of .text. Not to mention saving those "WTF is going on there... oh yeah, access_ok()" moments when looking through disassembly :) Cheers, Robin. > Signed-off-by: Arnd Bergmann > --- > arch/arm64/include/asm/uaccess.h | 28 +++++----------------------- > 1 file changed, 5 insertions(+), 23 deletions(-) > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > index 357f7bd9c981..e8dce0cc5eaa 100644 > --- a/arch/arm64/include/asm/uaccess.h > +++ b/arch/arm64/include/asm/uaccess.h > @@ -26,6 +26,8 @@ > #include > #include > > +static inline int __access_ok(const void __user *ptr, unsigned long size); > + > /* > * Test whether a block of memory is a valid user space address. > * Returns 1 if the range is valid, 0 otherwise. > @@ -33,10 +35,8 @@ > * This is equivalent to the following test: > * (u65)addr + (u65)size <= (u65)TASK_SIZE_MAX > */ > -static inline unsigned long __access_ok(const void __user *addr, unsigned long size) > +static inline int access_ok(const void __user *addr, unsigned long size) > { > - unsigned long ret, limit = TASK_SIZE_MAX - 1; > - > /* > * Asynchronous I/O running in a kernel thread does not have the > * TIF_TAGGED_ADDR flag of the process owning the mm, so always untag > @@ -46,27 +46,9 @@ static inline unsigned long __access_ok(const void __user *addr, unsigned long s > (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR))) > addr = untagged_addr(addr); > > - __chk_user_ptr(addr); > - asm volatile( > - // A + B <= C + 1 for all A,B,C, in four easy steps: > - // 1: X = A + B; X' = X % 2^64 > - " adds %0, %3, %2\n" > - // 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4 > - " csel %1, xzr, %1, hi\n" > - // 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X' > - // to compensate for the carry flag being set in step 4. For > - // X > 2^64, X' merely has to remain nonzero, which it does. > - " csinv %0, %0, xzr, cc\n" > - // 4: For X < 2^64, this gives us X' - C - 1 <= 0, where the -1 > - // comes from the carry in being clear. Otherwise, we are > - // testing X' - C == 0, subject to the previous adjustments. > - " sbcs xzr, %0, %1\n" > - " cset %0, ls\n" > - : "=&r" (ret), "+r" (limit) : "Ir" (size), "0" (addr) : "cc"); > - > - return ret; > + return likely(__access_ok(addr, size)); > } > -#define __access_ok __access_ok > +#define access_ok access_ok > > #include >