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 X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 048A2C433E1 for ; Mon, 29 Jun 2020 19:37:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9BB8206E2 for ; Mon, 29 Jun 2020 19:37:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593459428; bh=Dz13eb/rJGgeoaRVyWqs3XRGPmYfk43xXMq8OI26fbA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=bJ4FKSpyYEtvOh5XlQh3seE7+evFPFhFcbWdDv7CSH9P119yPxH4U9RLUi8ezF17r zAdZDeKKZRgQWDP+j5DuEmOoBywxg73LbKTtuOAsmu4+Yh7XVoGQsegBHa2LAC+POz ws//5X2u+2wajG7GvoqaK0t5H3wO4jVlbscEI7f4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731272AbgF2Tgn (ORCPT ); Mon, 29 Jun 2020 15:36:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:40598 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733017AbgF2Tae (ORCPT ); Mon, 29 Jun 2020 15:30:34 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EDE162529F; Mon, 29 Jun 2020 15:36:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593445009; bh=Dz13eb/rJGgeoaRVyWqs3XRGPmYfk43xXMq8OI26fbA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z8Mb36iTsHoqwIPO6Hv8NMp1GKDM2pzAA/CjKmHhMwAkE2x7pXeYMdOPWIllSpPn1 JlVFrzZjMwLNPeUafmPXlbgfgFL5/sfsOlks3VVTofNY3M5mozMRb9BB9zOy7zQjZq pPfMykz+tjKZjEYF978TkqdL6lpwMT+H3wPlN/wU= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Matt Fleming , Borislav Petkov , Greg Kroah-Hartman Subject: [PATCH 4.19 110/131] x86/asm/64: Align start of __clear_user() loop to 16-bytes Date: Mon, 29 Jun 2020 11:34:41 -0400 Message-Id: <20200629153502.2494656-111-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200629153502.2494656-1-sashal@kernel.org> References: <20200629153502.2494656-1-sashal@kernel.org> MIME-Version: 1.0 X-KernelTest-Patch: http://kernel.org/pub/linux/kernel/v4.x/stable-review/patch-4.19.131-rc1.gz X-KernelTest-Tree: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git X-KernelTest-Branch: linux-4.19.y X-KernelTest-Patches: git://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git X-KernelTest-Version: 4.19.131-rc1 X-KernelTest-Deadline: 2020-07-01T15:34+00:00 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Matt Fleming commit bb5570ad3b54e7930997aec76ab68256d5236d94 upstream. x86 CPUs can suffer severe performance drops if a tight loop, such as the ones in __clear_user(), straddles a 16-byte instruction fetch window, or worse, a 64-byte cacheline. This issues was discovered in the SUSE kernel with the following commit, 1153933703d9 ("x86/asm/64: Micro-optimize __clear_user() - Use immediate constants") which increased the code object size from 10 bytes to 15 bytes and caused the 8-byte copy loop in __clear_user() to be split across a 64-byte cacheline. Aligning the start of the loop to 16-bytes makes this fit neatly inside a single instruction fetch window again and restores the performance of __clear_user() which is used heavily when reading from /dev/zero. Here are some numbers from running libmicro's read_z* and pread_z* microbenchmarks which read from /dev/zero: Zen 1 (Naples) libmicro-file 5.7.0-rc6 5.7.0-rc6 5.7.0-rc6 revert-1153933703d9+ align16+ Time mean95-pread_z100k 9.9195 ( 0.00%) 5.9856 ( 39.66%) 5.9938 ( 39.58%) Time mean95-pread_z10k 1.1378 ( 0.00%) 0.7450 ( 34.52%) 0.7467 ( 34.38%) Time mean95-pread_z1k 0.2623 ( 0.00%) 0.2251 ( 14.18%) 0.2252 ( 14.15%) Time mean95-pread_zw100k 9.9974 ( 0.00%) 6.0648 ( 39.34%) 6.0756 ( 39.23%) Time mean95-read_z100k 9.8940 ( 0.00%) 5.9885 ( 39.47%) 5.9994 ( 39.36%) Time mean95-read_z10k 1.1394 ( 0.00%) 0.7483 ( 34.33%) 0.7482 ( 34.33%) Note that this doesn't affect Haswell or Broadwell microarchitectures which seem to avoid the alignment issue by executing the loop straight out of the Loop Stream Detector (verified using perf events). Fixes: 1153933703d9 ("x86/asm/64: Micro-optimize __clear_user() - Use immediate constants") Signed-off-by: Matt Fleming Signed-off-by: Borislav Petkov Cc: # v4.19+ Link: https://lkml.kernel.org/r/20200618102002.30034-1-matt@codeblueprint.co.uk Signed-off-by: Greg Kroah-Hartman --- arch/x86/lib/usercopy_64.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c index 9c5606d88f618..7077b3e282414 100644 --- a/arch/x86/lib/usercopy_64.c +++ b/arch/x86/lib/usercopy_64.c @@ -23,6 +23,7 @@ unsigned long __clear_user(void __user *addr, unsigned long size) asm volatile( " testq %[size8],%[size8]\n" " jz 4f\n" + " .align 16\n" "0: movq $0,(%[dst])\n" " addq $8,%[dst]\n" " decl %%ecx ; jnz 0b\n" -- 2.25.1