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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FB05C4167B for ; Thu, 30 Nov 2023 10:16:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231854AbjK3KQ1 (ORCPT ); Thu, 30 Nov 2023 05:16:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbjK3KQZ (ORCPT ); Thu, 30 Nov 2023 05:16:25 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2a07:de40:b251:101:10:150:64:2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0615910D0 for ; Thu, 30 Nov 2023 02:16:32 -0800 (PST) Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 5771F1FCEA; Thu, 30 Nov 2023 10:16:30 +0000 (UTC) Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 2A81913AB1; Thu, 30 Nov 2023 10:16:30 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id InggBv5gaGXEDAAAD6G6ig (envelope-from ); Thu, 30 Nov 2023 10:16:30 +0000 Date: Thu, 30 Nov 2023 11:16:29 +0100 From: Michal Hocko To: Baoquan He Cc: Donald Dutile , Jiri Bohac , Pingfan Liu , Tao Liu , Vivek Goyal , Dave Young , kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/4] kdump: crashkernel reservation from CMA Message-ID: References: <91a31ce5-63d1-7470-18f7-92b039fda8e6@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spamd-Bar: +++++++++++++++ Authentication-Results: smtp-out2.suse.de; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=suse.com (policy=quarantine); spf=fail (smtp-out2.suse.de: domain of mhocko@suse.com does not designate 2a07:de40:b281:104:10:150:64:97 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspamd-Server: rspamd2 X-Spamd-Result: default: False [15.00 / 50.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_SPF_FAIL(1.00)[-all]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MID_RHS_NOT_FQDN(0.50)[]; DMARC_POLICY_QUARANTINE(1.50)[suse.com : No valid SPF, No valid DKIM,quarantine]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_COUNT_THREE(0.00)[3]; MX_GOOD(-0.01)[]; RCPT_COUNT_SEVEN(0.00)[9]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(2.20)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-0.00)[12.74%] X-Rspamd-Queue-Id: 5771F1FCEA X-Spam: Yes Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 30-11-23 11:00:48, Baoquan He wrote: [...] > Now, we are worried if there's risk if the CMA area is retaken into kdump > kernel as system RAM. E.g is it possible that 1st kernel's ongoing RDMA > or DMA will interfere with kdump kernel's normal memory accessing? > Because kdump kernel usually only reset and initialize the needed > device, e.g dump target. Those unneeded devices will be unshutdown and > let go. I do not really want to discount your concerns but I am bit confused why this matters so much. First of all, if there is a buggy RDMA driver which doesn't use the proper pinning API (which would migrate away from the CMA) then what is the worst case? We will get crash kernel corrupted potentially and fail to take a proper kernel crash, right? Is this worrisome? Yes. Is it a real roadblock? I do not think so. The problem seems theoretical to me and it is not CMA usage at fault here IMHO. It is the said theoretical driver that needs fixing anyway. Now, it is really fair to mention that CMA backed crash kernel memory has some limitations - CMA reservation can only be used by the userspace in the primary kernel. If the size is overshot this might have negative impact on kernel allocations - userspace memory dumping in the crash kernel is fundamentally incomplete. Just my 2c -- Michal Hocko SUSE Labs