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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 BBA50C04ABB for ; Thu, 13 Sep 2018 13:38:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8136C20854 for ; Thu, 13 Sep 2018 13:38:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8136C20854 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729499AbeIMSsU (ORCPT ); Thu, 13 Sep 2018 14:48:20 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:59752 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727623AbeIMSsT (ORCPT ); Thu, 13 Sep 2018 14:48:19 -0400 Received: from localhost (ip-213-127-77-73.ip.prioritytelecom.net [213.127.77.73]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 5EFD2CF3; Thu, 13 Sep 2018 13:38:48 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Juergen Gross , Thomas Gleixner , Jan Beulich , Jason Andryuk , Boris Ostrovsky Subject: [PATCH 4.9 61/78] x86/pae: use 64 bit atomic xchg function in native_ptep_get_and_clear Date: Thu, 13 Sep 2018 15:31:48 +0200 Message-Id: <20180913131811.825920310@linuxfoundation.org> X-Mailer: git-send-email 2.19.0 In-Reply-To: <20180913131805.732342940@linuxfoundation.org> References: <20180913131805.732342940@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Juergen Gross commit b2d7a075a1ccef2fb321d595802190c8e9b39004 upstream. Using only 32-bit writes for the pte will result in an intermediate L1TF vulnerable PTE. When running as a Xen PV guest this will at once switch the guest to shadow mode resulting in a loss of performance. Use arch_atomic64_xchg() instead which will perform the requested operation atomically with all 64 bits. Some performance considerations according to: https://software.intel.com/sites/default/files/managed/ad/dc/Intel-Xeon-Scalable-Processor-throughput-latency.pdf The main number should be the latency, as there is no tight loop around native_ptep_get_and_clear(). "lock cmpxchg8b" has a latency of 20 cycles, while "lock xchg" (with a memory operand) isn't mentioned in that document. "lock xadd" (with xadd having 3 cycles less latency than xchg) has a latency of 11, so we can assume a latency of 14 for "lock xchg". Signed-off-by: Juergen Gross Reviewed-by: Thomas Gleixner Reviewed-by: Jan Beulich Tested-by: Jason Andryuk Signed-off-by: Boris Ostrovsky Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/pgtable-3level.h | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) --- a/arch/x86/include/asm/pgtable-3level.h +++ b/arch/x86/include/asm/pgtable-3level.h @@ -1,6 +1,8 @@ #ifndef _ASM_X86_PGTABLE_3LEVEL_H #define _ASM_X86_PGTABLE_3LEVEL_H +#include + /* * Intel Physical Address Extension (PAE) Mode - three-level page * tables on PPro+ CPUs. @@ -142,10 +144,7 @@ static inline pte_t native_ptep_get_and_ { pte_t res; - /* xchg acts as a barrier before the setting of the high bits */ - res.pte_low = xchg(&ptep->pte_low, 0); - res.pte_high = ptep->pte_high; - ptep->pte_high = 0; + res.pte = (pteval_t)arch_atomic64_xchg((atomic64_t *)ptep, 0); return res; }