On 17/10/2016 16:50, Radim Krčmář wrote: > 2016-10-17 07:47-0200, Marcelo Tosatti: >> On Fri, Oct 14, 2016 at 06:20:31PM -0300, Eduardo Habkost wrote: >>> I have been wondering: should we allow live migration with the >>> invtsc flag enabled, if TSC scaling is available on the >>> destination? >> >> TSC scaling and invtsc flag, yes. > > Yes, if we have well synchronized time between hosts, then we might be > able to migrate with a TSC shift that cannot be perceived by the guest. > > Unless the VM also has a migratable assigned PCI device that uses ART, > because we have no protocol to update the setting of ART (in CPUID), so > we should keep migration forbidden then. We don't publish the ART leaf at all, do we? >> 1) Migration: to host with different TSC frequency. > > We shouldn't have done this even now when emulating anything newer than > Pentium 4, because those CPUs have constant TSC, which only lacks the > guarantee that it doesn't stop in deep C-states: Right, but: >> since Linux guests use kvmclock and Windows guests use Hyper-V >> enlightenment, it should be fine to disable 2). ... and 1 too. We should also blacklist the TSC deadline timer when invtsc is not available. Paolo -- 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
