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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 28E12ECE566 for ; Fri, 21 Sep 2018 14:23:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC62B21547 for ; Fri, 21 Sep 2018 14:23:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC62B21547 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 S2390103AbeIUUMa (ORCPT ); Fri, 21 Sep 2018 16:12:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21740 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728313AbeIUUMa (ORCPT ); Fri, 21 Sep 2018 16:12:30 -0400 Received: from smtp.corp.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.26]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 13514C003EB7; Fri, 21 Sep 2018 14:23:23 +0000 (UTC) Received: from [10.36.117.43] (ovpn-117-43.ams2.redhat.com [10.36.117.43]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2A00930912F4; Fri, 21 Sep 2018 14:23:19 +0000 (UTC) Subject: Re: [PATCH V5 4/4] kvm: add a check if pfn is from NVDIMM pmem. To: Dan Williams , KVM list , Linux Kernel Mailing List , linux-nvdimm , Paolo Bonzini , Dave Jiang , "Zhang, Yu C" , Pankaj Gupta , Jan Kara , Christoph Hellwig , Linux MM , rkrcmar@redhat.com, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , "Zhang, Yi Z" References: <4e8c2e0facd46cfaf4ab79e19c9115958ab6f218.1536342881.git.yi.z.zhang@linux.intel.com> <20180920224953.GA53363@tiger-server> <20180921224739.GA33892@tiger-server> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: Date: Fri, 21 Sep 2018 16:23:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20180921224739.GA33892@tiger-server> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.26 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Fri, 21 Sep 2018 14:23:23 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/09/2018 00:47, Yi Zhang wrote: > On 2018-09-20 at 14:19:17 -0700, Dan Williams wrote: >> On Thu, Sep 20, 2018 at 7:11 AM Yi Zhang wrote: >>> >>> On 2018-09-19 at 09:20:25 +0200, David Hildenbrand wrote: >>>> Am 19.09.18 um 04:53 schrieb Dan Williams: >>>>> >>>>> Should we consider just not setting PageReserved for >>>>> devm_memremap_pages()? Perhaps kvm is not be the only component making >>>>> these assumptions about this flag? >>>> >>>> I was asking the exact same question in v3 or so. >>>> >>>> I was recently going through all PageReserved users, trying to clean up >>>> and document how it is used. >>>> >>>> PG_reserved used to be a marker "not available for the page allocator". >>>> This is only partially true and not really helpful I think. My current >>>> understanding: >>>> >>>> " >>>> PG_reserved is set for special pages, struct pages of such pages should >>>> in general not be touched except by their owner. Pages marked as >>>> reserved include: >>>> - Kernel image (including vDSO) and similar (e.g. BIOS, initrd) >>>> - Pages allocated early during boot (bootmem, memblock) >>>> - Zero pages >>>> - Pages that have been associated with a zone but were not onlined >>>> (e.g. NVDIMM/pmem, online_page_callback used by XEN) >>>> - Pages to exclude from the hibernation image (e.g. loaded kexec images) >>>> - MCA (memory error) pages on ia64 >>>> - Offline pages >>>> Some architectures don't allow to ioremap RAM pages that are not marked >>>> as reserved. Allocated pages might have to be set reserved to allow for >>>> that - if there is a good reason to enforce this. Consequently, >>>> PG_reserved part of a user space table might be the indicator for the >>>> zero page, pmem or MMIO pages. >>>> " >>>> >>>> Swapping code does not care about PageReserved at all as far as I >>>> remember. This seems to be fine as it only looks at the way pages have >>>> been mapped into user space. >>>> >>>> I don't really see a good reason to set pmem pages as reserved. One >>>> question would be, how/if to exclude them from the hibernation image. >>>> But that could also be solved differently (we would have to double check >>>> how they are handled in hibernation code). >>>> >>>> >>>> A similar user of PageReserved to look at is: >>>> >>>> drivers/vfio/vfio_iommu_type1.c:is_invalid_reserved_pfn() >>>> >>>> It will not mark pages dirty if they are reserved. Similar to KVM code. >>> Yes, kvm is not the only one user of the dax reserved page. >>>> >>>>> >>>>> Why is MEMORY_DEVICE_PUBLIC memory specifically excluded? >>>>> >>>>> This has less to do with "dax" pages and more to do with >>>>> devm_memremap_pages() established ranges. P2PDMA is another producer >>>>> of these pages. If either MEMORY_DEVICE_PUBLIC or P2PDMA pages can be >>>>> used in these kvm paths then I think this points to consider clearing >>>>> the Reserved flag. >>> >>> Thanks Dan/David's comments. >>> for MEMORY_DEVICE_PUBLIC memory, since host driver could manager the >>> memory resource to share to guest, Jerome says we could ignore it at >>> this time. >>> >>> And p2pmem, it seems mapped in a PCI bar space which should most likely >>> a mmio. I think kvm should treated as a reserved page. >> >> Ok, but the question you left unanswered is whether it would be better >> for devm_memremap_pages() to clear the PageReserved flag for >> MEMORY_DEVICE_{FS,DEV}_DAX rather than introduce a local kvm-only hack >> for what looks like a global problem. > > Remove the PageReserved flag sounds more reasonable. > And Could we still have a flag to identify it is a device private memory, or > where these pages coming from? We could use a page type for that or what you proposed. (as I said, we might have to change hibernation code to skip the pages once we drop the reserved flag). -- Thanks, David / dhildenb