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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 2C341C4321D for ; Thu, 23 Aug 2018 14:28:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1628206B6 for ; Thu, 23 Aug 2018 14:28:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D1628206B6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz 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 S1732278AbeHWR6V (ORCPT ); Thu, 23 Aug 2018 13:58:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:32954 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727597AbeHWR6U (ORCPT ); Thu, 23 Aug 2018 13:58:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id F2015ADD6; Thu, 23 Aug 2018 14:28:23 +0000 (UTC) From: Vlastimil Babka To: Thomas Gleixner , Ingo Molnar Cc: "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Andi Kleen , Dave Hansen , Michal Hocko , Vlastimil Babka , stable@vger.kernel.org, Michal Hocko Subject: [PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM Date: Thu, 23 Aug 2018 16:28:12 +0200 Message-Id: <20180823142812.7363-1-vbabka@suse.cz> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180823134418.17008-1-vbabka@suse.cz> References: <20180823134418.17008-1-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Two users have reported [1] that they have an "extremely unlikely" system with more than MAX_PA/2 memory and L1TF mitigation is not effective. Let's make the warning more helpful by suggesting the proper mem=X kernel boot param, a rough calculation of how much RAM can be lost (not precise if there's holes between MAX_PA/2 and max_pfn in the e820 map) and a link to the L1TF document to help decide if the mitigation is worth the unusable RAM. [1] https://bugzilla.suse.com/show_bug.cgi?id=1105536 Suggested-by: Michal Hocko Cc: stable@vger.kernel.org Signed-off-by: Vlastimil Babka --- arch/x86/kernel/cpu/bugs.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index cb4a16292aa7..4b820bb6c504 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -702,6 +702,11 @@ static void __init l1tf_select_mitigation(void) half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT; if (e820__mapped_any(half_pa, ULLONG_MAX - half_pa, E820_TYPE_RAM)) { pr_warn("System has more than MAX_PA/2 memory. L1TF mitigation not effective.\n"); + pr_info("You may make it effective by booting the kernel with mem=%llu parameter.\n", + half_pa); + pr_info("However, doing so will make up to %llu bytes of RAM unusable.\n", + ((u64) max_pfn << PAGE_SHIFT) - half_pa); + pr_info("Reading Documentation/admin-guide/l1tf.rst might help you decide."); return; } -- 2.18.0