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=-10.8 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 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 CF6C5C43219 for ; Wed, 20 Jan 2021 11:51:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98ACD23332 for ; Wed, 20 Jan 2021 11:51:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731181AbhATLhd (ORCPT ); Wed, 20 Jan 2021 06:37:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:40536 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729126AbhATKbT (ORCPT ); Wed, 20 Jan 2021 05:31:19 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611138608; 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=TEgO1GiA+c7h1rID5iKJ8FX+fU7rvgRZ7C7qLuJdxAY=; b=QHseIHGBZwT1U8a1+qwSPIYif1TxRiJNTDz4zgFPq4rwwayfaNyrfwPpFDe16HQdRc9+jW MpH3YLBsd7TVu3DpRayjJDsxjweSGfbv78TwjpYzzj8hwuMzB7MXTBMJlteMHCunWLFfab iX5YSThVs8TyNElXQMBoRNSbEQxcRxw= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 522FCAC97; Wed, 20 Jan 2021 10:30:08 +0000 (UTC) Date: Wed, 20 Jan 2021 11:30:07 +0100 From: Michal Hocko To: Dan Williams Cc: akpm@linux-foundation.org, David Hildenbrand , Oscar Salvador , linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 3/5] mm: Teach pfn_to_online_page() about ZONE_DEVICE section collisions Message-ID: <20210120103007.GH9371@dhcp22.suse.cz> References: <161058499000.1840162.702316708443239771.stgit@dwillia2-desk3.amr.corp.intel.com> <161058500675.1840162.7887862152161279354.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161058500675.1840162.7887862152161279354.stgit@dwillia2-desk3.amr.corp.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 13-01-21 16:43:26, 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()). > > While the memory map above is contrived via the memmap=ss!nn kernel > command line option, the collision happens in practice on shipping > platforms. The memory controller resources that decode spans of > physical address space are a limited resource. One technique > platform-firmware uses to conserve those resources is to share a decoder > across 2 devices to keep the address range contiguous. Unfortunately the > unit of operation of a decoder is 64MiB while the Linux section size is > 128MiB. This results in situations where, without subsection hotplug > memory mappings with different lifetimes collide into one object that > can only express one lifetime. Thank you this is a very useful insight to have in the changelog. > Update move_pfn_range_to_zone() to flag (SECTION_TAINT_ZONE_DEVICE) a > section that mixes ZONE_DEVICE pfns with other online pfns. With > SECTION_TAINT_ZONE_DEVICE to delineate, pfn_to_online_page() can fall > back to a slow-path check for ZONE_DEVICE pfns in an online section. In > the fast path online_section() for a full ZONE_DEVICE section returns > false. > > 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 > Reviewed-by: David Hildenbrand > Reviewed-by: Oscar Salvador > Signed-off-by: Dan Williams Acked-by: Michal Hocko I do not want to bikeshed but online_device_section is quite confusing. device_mixed_section would sound like a better name to me. -- Michal Hocko SUSE Labs