From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mario Smarduch Subject: Re: [RESEND PATCH v15 07/11] KVM: arm: page logging 2nd stage fault handling Date: Thu, 08 Jan 2015 08:28:46 -0800 Message-ID: <54AEB03E.8080305@samsung.com> References: <1418628488-3696-1-git-send-email-m.smarduch@samsung.com> <1418868449-23397-1-git-send-email-m.smarduch@samsung.com> <20150107123844.GA21092@cbox> <54ADE0B6.1060703@samsung.com> <20150108104510.GI21092@cbox> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: marc.zyngier@arm.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, pbonzini@redhat.com, catalin.marinas@arm.com To: Christoffer Dall Return-path: Received: from mailout2.w2.samsung.com ([211.189.100.12]:26439 "EHLO usmailout2.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754234AbbAHQ2v (ORCPT ); Thu, 8 Jan 2015 11:28:51 -0500 Received: from uscpsbgex4.samsung.com (u125.gpu85.samsung.co.kr [203.254.195.125]) by mailout2.w2.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0NHV00AXS9S1VB30@mailout2.w2.samsung.com> for kvm@vger.kernel.org; Thu, 08 Jan 2015 11:28:49 -0500 (EST) In-reply-to: <20150108104510.GI21092@cbox> Sender: kvm-owner@vger.kernel.org List-ID: On 01/08/2015 02:45 AM, Christoffer Dall wrote: > On Wed, Jan 07, 2015 at 05:43:18PM -0800, Mario Smarduch wrote: >> Hi Christoffer, >> before going through your comments, I discovered that >> in 3.18.0-rc2 - a generic __get_user_pages_fast() >> was implemented, now ARM picks this up. This causes >> gfn_to_pfn_prot() to return meaningful 'writable' >> value for a read fault, provided the region is writable. >> >> Prior to that the weak version returned 0 and 'writable' >> had no optimization effect to set pte/pmd - RW on >> a read fault. >> >> As a consequence dirty logging broke in 3.18, I was seeing Correction on this, proper __get_user_pages_fast() behavior exposed a bug in page logging code. >> weird but very intermittent issues. I just put in the >> additional few lines to fix it, prevent pte RW (only R) on >> read faults while logging writable region. >> >> On 01/07/2015 04:38 AM, Christoffer Dall wrote: >>> On Wed, Dec 17, 2014 at 06:07:29PM -0800, Mario Smarduch wrote: >>>> This patch is a followup to v15 patch series, with following changes: >>>> - When clearing/dissolving a huge, PMD mark huge page range dirty, since >>>> the state of whole range is unknown. After the huge page is dissolved >>>> dirty page logging is at page granularity. >>> >>> What is the sequence of events where you could have dirtied another page >>> within the PMD range after the user initially requested dirty page >>> logging? >> >> No there is none. My issue was the start point for tracking dirty pages >> and that would be second call to dirty log read. Not first >> call after initial write protect where any page in range can >> be assumed dirty. I'll remove this, not sure if there would be any >> use case to call dirty log only once. >> > > Calling dirty log once can not give you anything meaningful, right? You > must assume all memory is 'dirty' at this point, no? There is the interval between KVM_MEM_LOG_DIRTY_PAGES and first call to KVM_GET_DIRTY_LOG. Not sure of any use case, maybe enable logging, wait a while do a dirty log read, disable logging. Get an accumulated snapshot of dirty page activity. - Mario > > -Christoffer >