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=-12.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 BA1C1C2B9F8 for ; Tue, 25 May 2021 08:16:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9C14F61417 for ; Tue, 25 May 2021 08:16:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232153AbhEYISC (ORCPT ); Tue, 25 May 2021 04:18:02 -0400 Received: from mx2.suse.de ([195.135.220.15]:56944 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230370AbhEYISB (ORCPT ); Tue, 25 May 2021 04:18:01 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1621930591; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=cBTpb8oJt9glxSCHDQUwIyXY+s7ZBCa51c0d2hwY7nc=; b=EczqhsS4/Xi3ikRA8F8oPMZV5MYYAX6lPTn7KdzPl6WKUo7l+wWnC/B0mSH22rgXmtA055 kbLbdsKFvk65GV0LQe4n+vLdoQpePZu/j3Z4wWLqjiznCeXoRbgJ2pokf81wy9ezABhoY8 FBdCmL9X+POMWP7GrVxBuomgcWzVcoQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1621930591; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=cBTpb8oJt9glxSCHDQUwIyXY+s7ZBCa51c0d2hwY7nc=; b=5LG/R/yAUM5v9t0s1VF4gwLYCBRdG0N9ggk+VBmXNocCPcVfvBwWckPOqjt4TIl5jBI+pv nAJF0QhPxrXz9NCQ== Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 1C9ACAE1F; Tue, 25 May 2021 08:16:31 +0000 (UTC) Date: Tue, 25 May 2021 10:16:26 +0200 From: Oscar Salvador To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Andrew Morton , "Michael S. Tsirkin" , Jason Wang , Alexey Dobriyan , Mike Rapoport , "Matthew Wilcox (Oracle)" , 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 Subject: Re: [PATCH v2 4/6] mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline() Message-ID: <20210525081626.GB3300@linux> References: <20210514172247.176750-1-david@redhat.com> <20210514172247.176750-5-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210514172247.176750-5-david@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Fri, May 14, 2021 at 07:22:45PM +0200, David Hildenbrand wrote: > 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 > Signed-off-by: David Hildenbrand Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE L3