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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 3AF0BC433DB for ; Tue, 12 Jan 2021 11:01:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DEE682310D for ; Tue, 12 Jan 2021 11:01:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729134AbhALLBM (ORCPT ); Tue, 12 Jan 2021 06:01:12 -0500 Received: from mx2.suse.de ([195.135.220.15]:55310 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725922AbhALLBM (ORCPT ); Tue, 12 Jan 2021 06:01:12 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 1D567AD18; Tue, 12 Jan 2021 11:00:31 +0000 (UTC) Date: Tue, 12 Jan 2021 12:00:28 +0100 From: Oscar Salvador To: Dan Williams Cc: linux-mm@kvack.org, Andrew Morton , Michal Hocko , David Hildenbrand , vishal.l.verma@intel.com, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/5] mm: Teach pfn_to_online_page() about ZONE_DEVICE section collisions Message-ID: <20210112110028.GB12956@linux> References: <161044407603.1482714.16630477578392768273.stgit@dwillia2-desk3.amr.corp.intel.com> <161044409294.1482714.434561066315039753.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161044409294.1482714.434561066315039753.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 12, 2021 at 01:34:53AM -0800, Dan Williams wrote: > While pfn_to_online_page() is able to determine pfn_valid() at > subsection granularity it is not able to reliably determine if a given > pfn is also online if the section is mixes ZONE_{NORMAL,MOVABLE} with > ZONE_DEVICE. This means that pfn_to_online_page() may return invalid > @page objects. For example with a memory map like: > > 100000000-1fbffffff : System RAM > 142000000-143002e16 : Kernel code > 143200000-143713fff : Kernel rodata > 143800000-143b15b7f : Kernel data > 144227000-144ffffff : Kernel bss > 1fc000000-2fbffffff : Persistent Memory (legacy) > 1fc000000-2fbffffff : namespace0.0 > > This command: > > echo 0x1fc000000 > /sys/devices/system/memory/soft_offline_page > > ...succeeds when it should fail. When it succeeds it touches > an uninitialized page and may crash or cause other damage (see > dissolve_free_huge_page()). [...] > Because the collision case is rare, and for simplicity, the > SECTION_TAINT_ZONE_DEVICE flag is never cleared once set. > > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > Cc: Andrew Morton > Reported-by: Michal Hocko > Reported-by: David Hildenbrand > Signed-off-by: Dan Williams Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE L3