From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx2.suse.de ([195.135.220.15]) by Galois.linutronix.de with esmtps (TLS1.0:DHE_RSA_CAMELLIA_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1fEAVR-0005Lj-AW for speck@linutronix.de; Thu, 03 May 2018 11:26:33 +0200 Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 1814DAC9E for ; Thu, 3 May 2018 09:26:22 +0000 (UTC) Date: Thu, 3 May 2018 11:26:21 +0200 From: Michal Hocko Subject: [MODERATED] Re: Updated L1TF native OS patch Message-ID: <20180503092621.GE4535@dhcp22.suse.cz> References: <20180501234247.GA41910@tassilo.jf.intel.com> <20180502000512.GO75137@tassilo.jf.intel.com> <20180502012112.GQ75137@tassilo.jf.intel.com> <20180502121420.GB31258@dhcp22.suse.cz> <20180502150739.GS75137@tassilo.jf.intel.com> <20180502153554.GK26305@dhcp22.suse.cz> <20180502160813.GT75137@tassilo.jf.intel.com> MIME-Version: 1.0 In-Reply-To: <20180502160813.GT75137@tassilo.jf.intel.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit To: speck@linutronix.de List-ID: On Wed 02-05-18 09:08:13, speck for Andi Kleen wrote: > > > There's nothing the hypervisor can do about this. This > > > mitigation has to be done in the guest. > > > > > > > Patch 3 seems reasonable but I do not feel confident enough to give my > > > > ack because I simply have no idea whether some obscure HW depends on the > > > > zero page. > > > > > > Can you expand? How should hardware depend on it? > > > > > > It certainly cannot write to it, and even reading would be dubious because > > > the contents are undefined. > > > > Yeah, reads is what I would be worried about. I do not have any specific > > offender in mind but this is really hard to check for. > > There's no difference for reads. The memory does not go away. > It can still read it. > > The reservation just guarantees it is never used for any user data. Yeah, but I am not really sure some virtualization or crap HW has to have it allocated for RO. Maybe I am too paranoid. Anyway, I am not saying the patch is wrong, I am just not sure enough to give my ack. -- Michal Hocko SUSE Labs