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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 32720ECDFD3 for ; Thu, 13 Sep 2018 17:35:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 173E7217AE for ; Thu, 13 Sep 2018 17:17:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 173E7217AE 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 S1727728AbeIMW2F (ORCPT ); Thu, 13 Sep 2018 18:28:05 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:53336 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726747AbeIMW2E (ORCPT ); Thu, 13 Sep 2018 18:28:04 -0400 Received: from localhost (ip-213-127-77-73.ip.prioritytelecom.net [213.127.77.73]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id D84B3D09; Thu, 13 Sep 2018 17:17:38 +0000 (UTC) Date: Thu, 13 Sep 2018 19:17:14 +0200 From: Greg KH To: Jason Andryuk Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, jbeulich@suse.com, Juergen Gross , Boris Ostrovsky Subject: Re: [PATCH 4.14] x86/pae: use 64 bit atomic xchg function in native_ptep_get_and_clear Message-ID: <20180913171714.GA26169@kroah.com> References: <20180913155611.10854-1-jandryuk@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180913155611.10854-1-jandryuk@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 13, 2018 at 11:56:11AM -0400, Jason Andryuk wrote: > 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 > Atomic operations gained an arch_ prefix in commit > 8bf705d130396e69c04cd8e6e010244ad2ce71f4 > s/arch_atomic64_xchg/atomic64_xchg/ for backport. > Signed-off-by: Jason Andryuk Thanks for the fix, I've now queued it up everywhere and will push out -rc2 versions of this. greg k-h