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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
