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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 53014C43387 for ; Tue, 8 Jan 2019 09:16:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2050B2183F for ; Tue, 8 Jan 2019 09:16:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728484AbfAHJQq (ORCPT ); Tue, 8 Jan 2019 04:16:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44334 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728299AbfAHJQA (ORCPT ); Tue, 8 Jan 2019 04:16:00 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9FEEB89AE3; Tue, 8 Jan 2019 09:15:59 +0000 (UTC) Received: from [10.36.117.234] (ovpn-117-234.ams2.redhat.com [10.36.117.234]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9DEF4608DC; Tue, 8 Jan 2019 09:15:57 +0000 (UTC) Subject: Re: [PATCH] hv_balloon: avoid touching uninitialized struct page during tail onlining To: Vitaly Kuznetsov , devel@linuxdriverproject.org Cc: Sasha Levin , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , linux-kernel@vger.kernel.org, Dexuan Cui References: <20190104141942.19126-1-vkuznets@redhat.com> <2ea7e975-6aae-de71-83e5-9302518802ef@redhat.com> <87d0p837lt.fsf@vitty.brq.redhat.com> 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: <39a3ac32-6569-d19f-c87c-da6d72251748@redhat.com> Date: Tue, 8 Jan 2019 10:15:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <87d0p837lt.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 08 Jan 2019 09:15:59 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07.01.19 14:44, Vitaly Kuznetsov wrote: > David Hildenbrand writes: > >> On 04.01.19 15:19, Vitaly Kuznetsov wrote: >>> Hyper-V memory hotplug protocol has 2M granularity and in Linux x86 we use >>> 128M. To deal with it we implement partial section onlining by registering >>> custom page onlining callback (hv_online_page()). Later, when more memory >>> arrives we try to online the 'tail' (see hv_bring_pgs_online()). >>> >>> It was found that in some cases this 'tail' onlining causes issues: >>> >>> BUG: Bad page state in process kworker/0:2 pfn:109e3a >>> page:ffffe08344278e80 count:0 mapcount:1 mapping:0000000000000000 index:0x0 >>> flags: 0xfffff80000000() >>> raw: 000fffff80000000 dead000000000100 dead000000000200 0000000000000000 >>> raw: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 >>> page dumped because: nonzero mapcount >>> ... >>> Workqueue: events hot_add_req [hv_balloon] >>> Call Trace: >>> dump_stack+0x5c/0x80 >>> bad_page.cold.112+0x7f/0xb2 >>> free_pcppages_bulk+0x4b8/0x690 >>> free_unref_page+0x54/0x70 >>> hv_page_online_one+0x5c/0x80 [hv_balloon] >>> hot_add_req.cold.24+0x182/0x835 [hv_balloon] >>> ... >>> >>> Turns out that we now have deferred struct page initialization for memory >>> hotplug so e.g. memory_block_action() in drivers/base/memory.c does >>> pages_correctly_probed() check and in that check it avoids inspecting >>> struct pages and checks sections instead. But in Hyper-V balloon driver we >>> do PageReserved(pfn_to_page()) check and this is now wrong. >>> >>> Switch to checking online_section_nr() instead. >>> >>> Signed-off-by: Vitaly Kuznetsov >>> --- >>> drivers/hv/hv_balloon.c | 10 ++++++---- >>> 1 file changed, 6 insertions(+), 4 deletions(-) >>> >>> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c >>> index 5301fef16c31..7c6349a50ef1 100644 >>> --- a/drivers/hv/hv_balloon.c >>> +++ b/drivers/hv/hv_balloon.c >>> @@ -888,12 +888,14 @@ static unsigned long handle_pg_range(unsigned long pg_start, >>> pfn_cnt -= pgs_ol; >>> /* >>> * Check if the corresponding memory block is already >>> - * online by checking its last previously backed page. >>> - * In case it is we need to bring rest (which was not >>> - * backed previously) online too. >>> + * online. It is possible to observe struct pages still >>> + * being uninitialized here so check section instead. >>> + * In case the section is online we need to bring the >>> + * rest of pfns (which were not backed previously) >>> + * online too. >>> */ >>> if (start_pfn > has->start_pfn && >>> - !PageReserved(pfn_to_page(start_pfn - 1))) >>> + online_section_nr(pfn_to_section_nr(start_pfn))) >>> hv_bring_pgs_online(has, start_pfn, pgs_ol); >>> >>> } >>> >> >> I wonder if you should use pfn_to_online_page() and check for PageOffline(). >> >> (I guess online_section_nr() should also do the trick) > > I'm worried a bit about racing with mm code here as we're not doing > mem_hotplug_begin()/done() so I'd slightly prefer keeping > online_section_nr() (pfn_to_online_page() also uses it but then it gets > to the particular struct page). Moreover, with pfn_to_online_page() we > will be looking at some other pfn - because the start_pfn is definitelly > offline (pre-patch we were looking at start_pfn-1). Just looking at the > whole section seems cleaner. Fine with me. I guess the section can never be offlined as it still contains reserved pages if not fully "fake-onlined" by HV code already. But we could still consider mem_hotplug_begin()/done() as we could have a online section although online_pages() has not completed yet. So we could actually touch some "semi onlined section". Acked-by: David Hildenbrand > > P.S. I still think about bringing mem_hotplug_begin()/done() to > hv_balloon but that's going to be a separate discussion, here I want to > have a small fix backportable to stable. > > Thanks, > -- Thanks, David / dhildenb