On 16/03/2018 16:40, Vitaly Kuznetsov wrote: >> On older kernel without re-enlightenment support, you don't want to >> expose the frequency MSRs unless invtsc is on, right? >> > Actually no, I think it's OK to expose frequency MSRs even when we don't > have invtsc and don't support re-enlightenment. Nested Hyper-V won't > pass stable TSC pages to its guests unless it sees either invtsc or > reenlightenment. So as long as we have something to put to these MSRs > (env->tsc_khz) I *think* we can expose them. > > I may actually be missing the reason why Ladi put > tsc_is_stable_and_known() here.
Probably because I asked him to. :) It looks like Hyper-V knows that you need re-enlightenment in order to really trust the frequency MSRs (of course the TSC page is special because it has the sequence count). So the patch is good. Thanks! Paolo > In case we're running Windows (and not > Hyper-V) as a guest KVM will update TSC page on migration. And genuine > Hyper-V also exposes these MSRs without exposing INVTSC flag by > default.
