On 12/26/2011 10:11 AM, Liu, Jinsong wrote: > > > > It breaks live migration: if you start a guest on a TSC-deadline > > capable host kernel, and migrate it to a TSC-deadline incapable host > > kernel, you end up with a broken guest. > > > > More broadly, kvm never exposes features transparently to the guest, > > it always passes them to userspace first, so userspace controls the > > ABI exposed to the guest. This prevents the following scenario: > > Do you mean, by the method qemu control cpuid exposing, it can avoid live migration broken issue by > 1. user probe the lowest ability host of whole pool where vm may live migrate; > 2. only if the lowest ablility host support the feature can user enable the feature when boot a vm; > 3. if the lowest ability host didn't support the feature (say tsc deadline timer as example), user disable the feature when boot a vm; > In this way, live migration wouldn't be broken. Right? Right. > or, do you mean qemu-kvm solve live migration broken issue by some other method? The method you outlined, or any other method, such as partitioning the cluster according to hardware capabilities. > > > > > - a guest is started on some hardware, which doesn't support some > > cpuid feature (say AVX for example) > > - the guest or one of its applications are broken wrt AVX, but because > > the feature is not exposed, it works correctly > > - the host hardware is upgraded to one which supports AVX > > - the guest is now broken > > You mean, live migrate from 'old' (which doesn't support the feature) platform to 'new' platform would broken? Live migration, or even just a guest restart on updated hardware. -- error compiling committee.c: too many arguments to function -- 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
