From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:59496 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726083AbeHWW47 (ORCPT ); Thu, 23 Aug 2018 18:56:59 -0400 Date: Thu, 23 Aug 2018 21:25:47 +0200 From: Michal Hocko To: Andi Kleen Cc: Vlastimil Babka , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Dave Hansen , stable@vger.kernel.org Subject: Re: [PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM Message-ID: <20180823192547.GS29735@dhcp22.suse.cz> References: <20180823134418.17008-1-vbabka@suse.cz> <20180823142812.7363-1-vbabka@suse.cz> <20180823154648.GD12066@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180823154648.GD12066@tassilo.jf.intel.com> Sender: stable-owner@vger.kernel.org List-ID: On Thu 23-08-18 08:46:48, Andi Kleen wrote: > On Thu, Aug 23, 2018 at 04:28:12PM +0200, 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. > > I'm not sure anyone would really do that. After all you probably prefer > your memory. And if it's really a non ECC client part they are are > already used to to live very dangerously because their undetected RAM bit error > rate will be significant. L1TF is probably one of your smaller problems > in this case... There are people who care about L1TF mitigations. I am not going to question their motivation. In any case a hint how to make the mitigation active again sounds more useful than something that sounds as scary as "you are vulnerable". -- Michal Hocko SUSE Labs