From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 0/8] use jump labels to streamline common APIC configuration Date: Tue, 14 Aug 2012 16:13:17 +0200 Message-ID: <502A5CFD.8080604@siemens.com> References: <1344171513-4659-1-git-send-email-gleb@redhat.com> <501E760E.9050109@redhat.com> <20120805133549.GL27579@redhat.com> <501E7839.2030008@redhat.com> <20120805134842.GM27579@redhat.com> <501E7C85.70001@redhat.com> <20120805140305.GN27579@redhat.com> <502A5A16.6040506@siemens.com> <502A5AE0.3080608@redhat.com> <20120814140701.GN11194@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , "kvm@vger.kernel.org" , "mtosatti@redhat.com" To: Gleb Natapov Return-path: Received: from goliath.siemens.de ([192.35.17.28]:25241 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954Ab2HNONW (ORCPT ); Tue, 14 Aug 2012 10:13:22 -0400 In-Reply-To: <20120814140701.GN11194@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2012-08-14 16:07, Gleb Natapov wrote: > On Tue, Aug 14, 2012 at 05:04:16PM +0300, Avi Kivity wrote: >> On 08/14/2012 05:00 PM, Jan Kiszka wrote: >> >>>>> The host can prevent this by leaving disabling the guest pmu. But >>>>> disabling jump labels for real-time kernels may be acceptable too. We >>>>> can probably to it at run time by forcing the slow path at all times. >>>> Yes, it is possible to add module option that will force slow path if >>>> needed. >>> >>> Should I write a patch or will you? Having host-side stop_machine due to >>> such common guest operations is indeed a no-go for RT. >>> >> >> Note that an additional patch is needed for perf, otherwise the guest >> (or a user, but that's less of a concern for realtime) can easily invoke >> stop_machine by configuring and unconfiguring its pmu. >> >> > Are we talking about malicious guests? Why not compile kernel with jump > label disabled if this is serious concern? Because jump labels are still useful for other purposes (e.g. tracing) - provided you don't use them while a critical operation is running. It's cumbersome to require static configuration, specifically given that we could easily control dynamically it at KVM level. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux