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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 34356C433F4 for ; Thu, 30 Aug 2018 12:39:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E6FAF205F4 for ; Thu, 30 Aug 2018 12:39:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E6FAF205F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728866AbeH3QlP (ORCPT ); Thu, 30 Aug 2018 12:41:15 -0400 Received: from mga07.intel.com ([134.134.136.100]:55181 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728849AbeH3QlP (ORCPT ); Thu, 30 Aug 2018 12:41:15 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 30 Aug 2018 05:39:17 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,306,1531810800"; d="scan'208";a="86236124" Received: from shbuild888.sh.intel.com (HELO localhost) ([10.239.146.239]) by orsmga001.jf.intel.com with ESMTP; 30 Aug 2018 05:39:16 -0700 Date: Thu, 30 Aug 2018 20:43:42 +0800 From: Feng Tang To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Yinghai Lu , Dave Hansen , Andi Kleen Subject: Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for NO_BOOTMEM Message-ID: <20180830124342.ehtv7v4xszvmgpia@shbuild888> References: <20180830090319.985-1-feng.tang@intel.com> <20180830104401.GZ24124@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180830104401.GZ24124@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On Thu, Aug 30, 2018 at 12:44:02PM +0200, Peter Zijlstra wrote: > On Thu, Aug 30, 2018 at 05:03:19PM +0800, Feng Tang wrote: > > We hit a kernel panic when enabling earlycon for a platform, the > > call trace is: > > > > panic+0xd2/0x220 > > __alloc_bootmem+0x31/0x34 > > spp_getpage+0x60/0x8a > > fill_pte+0x71/0x130 > > __set_pte_vaddr+0x1d/0x50 > > set_pte_vaddr+0x3c/0x60 > > __native_set_fixmap+0x23/0x30 > > native_set_fixmap+0x30/0x40 > > setup_earlycon+0x1e0/0x32f > > param_setup_earlycon+0x13/0x22 > > do_early_param+0x5b/0x90 > > parse_args+0x1f7/0x300 > > parse_early_options+0x24/0x28 > > parse_early_param+0x65/0x73 > > setup_arch+0x31e/0x9f1 > > start_kernel+0x58/0x44e > > > > The root cause is that when CONFIG_NO_BOOTMEM=y, before > > e820__memblock_setup() is called there is no memory for bootmem > > to allocate, > > Which you bloody well asked for by using NO_BOOTMEM=y. > > Going down this route; adding hacks for every little thing that does > want bootmem, completely defeats the purpose. > > If anything, make the earlycon thing depend on NO_BOOTMEM=n. That also > solves your problem. No earlycon, no panic. In current x86, the NO_BOOTMEM is "y" by default, and almost all the servers/desktops I could access have CONFIG_BOOTMEM=y, while earlycon is important for enabling new platforms, as well as kernel debugging. IMHO, it's better to keep earlycon capability. Also any alloc_bootmem() call in that time window will trigger panic. Thanks, Feng