From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH 0/8] use jump labels to streamline common APIC configuration Date: Tue, 14 Aug 2012 17:07:01 +0300 Message-ID: <20120814140701.GN11194@redhat.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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kiszka , "kvm@vger.kernel.org" , "mtosatti@redhat.com" To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:2435 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755191Ab2HNOHF (ORCPT ); Tue, 14 Aug 2012 10:07:05 -0400 Content-Disposition: inline In-Reply-To: <502A5AE0.3080608@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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? -- Gleb.