From patchwork Wed May 26 09:30:39 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 12281095 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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,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 AE5D5C2B9F7 for ; Wed, 26 May 2021 09:31:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4AD68613E6 for ; Wed, 26 May 2021 09:31:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4AD68613E6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E2FEA6B0070; Wed, 26 May 2021 05:31:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DB5B76B0071; Wed, 26 May 2021 05:31:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C08726B0072; Wed, 26 May 2021 05:31:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0057.hostedemail.com [216.40.44.57]) by kanga.kvack.org (Postfix) with ESMTP id 898286B0070 for ; Wed, 26 May 2021 05:31:34 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 281AF9885 for ; Wed, 26 May 2021 09:31:34 +0000 (UTC) X-FDA: 78182864508.28.1DBED86 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf23.hostedemail.com (Postfix) with ESMTP id C3E84A0001C1 for ; Wed, 26 May 2021 09:31:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622021493; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0LN0J8fOWqC6Tk5wkSbpwkNZtNpLvOB+CwQIFMbUdeo=; b=AnIppB8NgblNZ0a7jsbJMwU4h5WyngA5mcaVh/bYm038pee2Ynh2AHzYYiZmMRPTLbdED7 f+U/pL6mfMWmTArjT3FNy7MBw/UyfydjHOTWalvyR+qwWZgpaI+rXhNZQj9ZHcharl2e+4 I/t+TVHMfQL+h54WSNz4h4FhQn7yoss= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-574-gnXabOTcN2GlrtYNjLBgrQ-1; Wed, 26 May 2021 05:31:31 -0400 X-MC-Unique: gnXabOTcN2GlrtYNjLBgrQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0899D107ACE3; Wed, 26 May 2021 09:31:29 +0000 (UTC) Received: from t480s.redhat.com (ovpn-113-99.ams2.redhat.com [10.36.113.99]) by smtp.corp.redhat.com (Postfix) with ESMTP id 892915D9D3; Wed, 26 May 2021 09:31:23 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , Andrew Morton , "Michael S. Tsirkin" , Jason Wang , Alexey Dobriyan , Mike Rapoport , "Matthew Wilcox (Oracle)" , Oscar Salvador , Michal Hocko , Roman Gushchin , Alex Shi , Steven Price , Mike Kravetz , Aili Yao , Jiri Bohac , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Naoya Horiguchi , linux-hyperv@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Mike Rapoport Subject: [PATCH v3 4/6] mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline() Date: Wed, 26 May 2021 11:30:39 +0200 Message-Id: <20210526093041.8800-5-david@redhat.com> In-Reply-To: <20210526093041.8800-1-david@redhat.com> References: <20210526093041.8800-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Rspamd-Queue-Id: C3E84A0001C1 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AnIppB8N; spf=none (imf23.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam04 X-Stat-Signature: s1y8ywyzcy33x8hdm78ebibd6ugu3wxi X-HE-Tag: 1622021487-368933 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: A driver might set a page logically offline -- PageOffline() -- and turn the page inaccessible in the hypervisor; after that, access to page content can be fatal. One example is virtio-mem; while unplugged memory -- marked as PageOffline() can currently be read in the hypervisor, this will no longer be the case in the future; for example, when having a virtio-mem device backed by huge pages in the hypervisor. Some special PFN walkers -- i.e., /proc/kcore -- read content of random pages after checking PageOffline(); however, these PFN walkers can race with drivers that set PageOffline(). Let's introduce page_offline_(begin|end|freeze|thaw) for synchronizing. page_offline_freeze()/page_offline_thaw() allows for a subsystem to synchronize with such drivers, achieving that a page cannot be set PageOffline() while frozen. page_offline_begin()/page_offline_end() is used by drivers that care about such races when setting a page PageOffline(). For simplicity, use a rwsem for now; neither drivers nor users are performance sensitive. Acked-by: Michal Hocko Reviewed-by: Mike Rapoport Reviewed-by: Oscar Salvador Signed-off-by: David Hildenbrand --- include/linux/page-flags.h | 10 ++++++++++ mm/util.c | 40 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index daed82744f4b..382464aa3c20 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -769,9 +769,19 @@ PAGE_TYPE_OPS(Buddy, buddy) * relies on this feature is aware that re-onlining the memory block will * require to re-set the pages PageOffline() and not giving them to the * buddy via online_page_callback_t. + * + * There are drivers that mark a page PageOffline() and expect there won't be + * any further access to page content. PFN walkers that read content of random + * pages should check PageOffline() and synchronize with such drivers using + * page_offline_freeze()/page_offline_thaw(). */ PAGE_TYPE_OPS(Offline, offline) +extern void page_offline_freeze(void); +extern void page_offline_thaw(void); +extern void page_offline_begin(void); +extern void page_offline_end(void); + /* * Marks pages in use as page tables. */ diff --git a/mm/util.c b/mm/util.c index a8bf17f18a81..a034525e7ba2 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1010,3 +1010,43 @@ void mem_dump_obj(void *object) } EXPORT_SYMBOL_GPL(mem_dump_obj); #endif + +/* + * A driver might set a page logically offline -- PageOffline() -- and + * turn the page inaccessible in the hypervisor; after that, access to page + * content can be fatal. + * + * Some special PFN walkers -- i.e., /proc/kcore -- read content of random + * pages after checking PageOffline(); however, these PFN walkers can race + * with drivers that set PageOffline(). + * + * page_offline_freeze()/page_offline_thaw() allows for a subsystem to + * synchronize with such drivers, achieving that a page cannot be set + * PageOffline() while frozen. + * + * page_offline_begin()/page_offline_end() is used by drivers that care about + * such races when setting a page PageOffline(). + */ +static DECLARE_RWSEM(page_offline_rwsem); + +void page_offline_freeze(void) +{ + down_read(&page_offline_rwsem); +} + +void page_offline_thaw(void) +{ + up_read(&page_offline_rwsem); +} + +void page_offline_begin(void) +{ + down_write(&page_offline_rwsem); +} +EXPORT_SYMBOL(page_offline_begin); + +void page_offline_end(void) +{ + up_write(&page_offline_rwsem); +} +EXPORT_SYMBOL(page_offline_end);