Roman Kagan <rkagan@xxxxxxxxxxxxx> writes: > On Wed, Feb 28, 2018 at 02:43:59PM +0100, Vitaly Kuznetsov wrote: >> Nested Hyper-V/Windows guest running on top of KVM will use TSC page >> clocksource in two cases: >> - L0 exposes invariant TSC (CPUID.80000007H:EDX[8]). >> - L0 provides Hyper-V Reenlightenment support (CPUID.40000003H:EAX[13]). >> >> Exposing invariant TSC effectively blocks migration to hosts with different >> TSC frequencies, > > I wonder if TSC scaling on the destination host doesn't allow to relax > this requirement? I don't see why it wouldn't, Skylake+ should be fine (but this, of course, will limit possible destination hosts to those supporting the feature -- even if no other CPU features are required). >> providing reenlightenment support will be needed when we >> start migrating nested workloads. >> >> Implement rudimentary support for reenlightenment MSRs. For now, these are >> just read/write MSRs with no effect. >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> >> --- >> arch/x86/include/asm/kvm_host.h | 4 ++++ >> arch/x86/kvm/hyperv.c | 21 +++++++++++++++++++++ >> arch/x86/kvm/x86.c | 12 +++++++++++- >> 3 files changed, 36 insertions(+), 1 deletion(-) > > Reviewed-by: Roman Kagan <rkagan@xxxxxxxxxxxxx> Thanks! -- Vitaly
