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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 67A37C4321D for ; Thu, 23 Aug 2018 19:27:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 23F7920841 for ; Thu, 23 Aug 2018 19:27:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 23F7920841 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1726835AbeHWW6V (ORCPT ); Thu, 23 Aug 2018 18:58:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:59684 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726083AbeHWW6V (ORCPT ); Thu, 23 Aug 2018 18:58:21 -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 4EE2EAEC0; Thu, 23 Aug 2018 19:27:11 +0000 (UTC) Date: Thu, 23 Aug 2018 21:27:09 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Andi Kleen , Dave Hansen , stable@vger.kernel.org Subject: Re: [PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM Message-ID: <20180823192709.GT29735@dhcp22.suse.cz> References: <20180823134418.17008-1-vbabka@suse.cz> <20180823142812.7363-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180823142812.7363-1-vbabka@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 23-08-18 16:28:12, Vlastimil Babka wrote: > 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 I wouldn't bother with max_pfn-half_pa part but other than that this is much more useful than the original message. Acked-by: Michal Hocko > --- > 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 -- Michal Hocko SUSE Labs