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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 49B91C4646D for ; Fri, 10 Aug 2018 13:28:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0F46223DB for ; Fri, 10 Aug 2018 13:28:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F0F46223DB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1728069AbeHJP57 (ORCPT ); Fri, 10 Aug 2018 11:57:59 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:53846 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727341AbeHJP57 (ORCPT ); Fri, 10 Aug 2018 11:57:59 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E125440241C8; Fri, 10 Aug 2018 13:28:02 +0000 (UTC) Received: from [10.36.116.247] (ovpn-116-247.ams2.redhat.com [10.36.116.247]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7A997215670D; Fri, 10 Aug 2018 13:28:00 +0000 (UTC) Subject: Re: [PATCH V3 0/4] Fix kvm misconceives NVDIMM pages as reserved mmio To: Zhang Yi , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, pbonzini@redhat.com, dan.j.williams@intel.com, jack@suse.cz, hch@lst.de, yu.c.zhang@intel.com Cc: linux-mm@kvack.org, rkrcmar@redhat.com, yi.z.zhang@intel.com References: From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.7]); Fri, 10 Aug 2018 13:28:02 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.7]); Fri, 10 Aug 2018 13:28:02 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'david@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09.08.2018 12:52, Zhang Yi wrote: > For device specific memory space, when we move these area of pfn to > memory zone, we will set the page reserved flag at that time, some of > these reserved for device mmio, and some of these are not, such as > NVDIMM pmem. > > Now, we map these dev_dax or fs_dax pages to kvm for DIMM/NVDIMM > backend, since these pages are reserved. the check of > kvm_is_reserved_pfn() misconceives those pages as MMIO. Therefor, we > introduce 2 page map types, MEMORY_DEVICE_FS_DAX/MEMORY_DEVICE_DEV_DAX, > to indentify these pages are from NVDIMM pmem. and let kvm treat these > as normal pages. > > Without this patch, Many operations will be missed due to this > mistreatment to pmem pages. For example, a page may not have chance to > be unpinned for KVM guest(in kvm_release_pfn_clean); not able to be > marked as dirty/accessed(in kvm_set_pfn_dirty/accessed) etc. > I am right now looking into (and trying to better document) PG_reserved - and having a hard time :) . One of the main points about reserved pages is that the struct pages are not to be touched. See [1] (I know that statement is fairly old, but it resembles what PG_reserved is actually used for nowadays - with some exceptions unfortunately.). Struct pages part of user space tables that are PG_reserved can indicate (as of now according to my research) - MMIO pages - Selected MMAPed pages - e.g. vDSO - Zero page - PMEM pages as you correctly state So I wonder, if it is really the right approach to silently go ahead and treat reserved pages just like they would not be reserved. Maybe the right approach would rather be to do something about pmem pages being reserved. Yes, they are never to be given to the page allocator, but I wonder if PG_reserved is strictly needed for that. [1] https://lists.linuxcoding.com/kernel/2005-q3/msg10350.html > V1: > https://lkml.org/lkml/2018/7/4/91 > > V2: > https://lkml.org/lkml/2018/7/10/135 > > V3: > [PATCH V3 1/4] Needs Comments. > [PATCH V3 2/4] Update the description of MEMORY_DEVICE_DEV_DAX: Jan > [PATCH V3 3/4] Acked-by: Jan in V2 > [PATCH V3 4/4] Needs Comments. > > Zhang Yi (4): > kvm: remove redundant reserved page check > mm: introduce memory type MEMORY_DEVICE_DEV_DAX > mm: add a function to differentiate the pages is from DAX device > memory > kvm: add a check if pfn is from NVDIMM pmem. > > drivers/dax/pmem.c | 1 + > include/linux/memremap.h | 8 ++++++++ > include/linux/mm.h | 12 ++++++++++++ > virt/kvm/kvm_main.c | 16 ++++++++-------- > 4 files changed, 29 insertions(+), 8 deletions(-) > -- Thanks, David / dhildenb