From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751753AbaIYIwG (ORCPT ); Thu, 25 Sep 2014 04:52:06 -0400 Received: from mail.skyhub.de ([78.46.96.112]:46763 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750774AbaIYIwD (ORCPT ); Thu, 25 Sep 2014 04:52:03 -0400 Date: Thu, 25 Sep 2014 10:51:58 +0200 From: Borislav Petkov To: Henrique de Moraes Holschuh Cc: Chuck Ebbert , Andy Lutomirski , "H. Peter Anvin" , "linux-kernel@vger.kernel.org" Subject: Re: x86, microcode: BUG: microcode update that changes x86_capability Message-ID: <20140925085158.GF22317@nazgul.tnic> References: <20140918200659.GA5331@khazad-dum.debian.net> <20140919001311.GB5331@khazad-dum.debian.net> <20140919110014.GC29639@khazad-dum.debian.net> <20140919112953.GA3256@nazgul.tnic> <20140919075415.5149d5f2@as> <20140919150042.GC5318@nazgul.tnic> <20140919164217.GD17456@khazad-dum.debian.net> <20140923200054.GB16467@pd.tnic> <20140924145658.GB31678@khazad-dum.debian.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20140924145658.GB31678@khazad-dum.debian.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 24, 2014 at 11:56:58AM -0300, Henrique de Moraes Holschuh wrote: > I don't know about AMD, but on Intel, the time it takes to update the > microcode on a core is anything but negligible[1], so the microcode > version skew window still exists, and it is not small. It is much smaller > than it once was, but it is still there. I think that window is unsafe but yeah, we probably should take your empirical observation as good enough for now. > But IMHO we still need to detect and do something smart when > x86_capability changes due to a microcode update. > > And I'd really prefer it to be "update x86_capability, warn the user and > carry on" for anything that is not going to crash the kernel. The problem is with hiding CPUID bits and userspace using HLE after having detected it previously. I think we'll be on the safe side if we reboot thus the suggestion to the user that rebooting should be done ASAP. -- Regards/Gruss, Boris. --