From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47361) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eZG1U-0002Qj-Sc for qemu-devel@nongnu.org; Wed, 10 Jan 2018 08:02:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eZG1P-0000KH-77 for qemu-devel@nongnu.org; Wed, 10 Jan 2018 08:02:28 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50855) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eZG1P-0000Jz-07 for qemu-devel@nongnu.org; Wed, 10 Jan 2018 08:02:23 -0500 Date: Wed, 10 Jan 2018 13:02:05 +0000 From: "Daniel P. Berrange" Message-ID: <20180110130205.GN3205@redhat.com> Reply-To: "Daniel P. Berrange" References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] how to pass pcid to guest? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: Stefan Priebe - Profihost AG , qemu-devel On Mon, Jan 08, 2018 at 04:07:53PM -0600, Eric Blake wrote: > On 01/08/2018 02:03 PM, Stefan Priebe - Profihost AG wrote: > > Hello, > > > > for meltdown mitigation and performance it's important to have the pcid > > flag passed down to the guest (f.e. > > https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU). > > Indeed; you are still waiting on the qemu patch mentioned here: > https://www.qemu.org/2018/01/04/spectre/ > > which is still undergoing the review process, but should be up (in the > form of 2.11.1) "in the next few days". There's two different things here. The Spectre patch you mention is about exposing a new CPUID feature 'ibrs' that is added to fix Spectre. The 'pcid' feature Stefan mentions is a pre-existing feature that is not a security fix, but rather a way to improve the performance when the KAISER/KPTI patches are enabled for Meltdown. 'pcid' is available in QEMU's Haswell, Broadwell & Skylake based CPU models by default. For other named CPU models, you can turn it on using ',+pcid' after the model name. eg '-cpu Westmere,+pcid' (as long as your host supports it of course) Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|