[libvirt] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc)

On Wed, Jan 04, 2017 at 09:56:56AM -0200, Marcelo Tosatti wrote: > On Tue, Dec 27, 2016 at 05:21:20PM -0200, Eduardo Habkost wrote: > > Instead of blocking migration on the source when invtsc is > > enabled, rely on the migration destination to ensure there's no > > TSC frequency mismatch. > > > > We can't allow migration unconditionally because we don't know if > > the destination is a QEMU version that is really going to ensure > > there's no TSC frequency mismatch. To ensure we are migrating to > > a destination that won't ignore SET_TSC_KHZ errors, allow invtsc > > migration only on pc-*-2.9 and newer. > > > > Signed-off-by: Eduardo Habkost <ehabkost(a)redhat.com&gt;

> > @@ -2655,12 +2656,14 @@ int kvm_arch_put_registers(CPUState *cpu, int level) > > } > > > > if (level == KVM_PUT_FULL_STATE) { > > - /* We don't check for kvm_arch_set_tsc_khz() errors here, > > - * because TSC frequency mismatch shouldn't abort migration, > > - * unless the user explicitly asked for a more strict TSC > > - * setting (e.g. using an explicit "tsc-freq" option). > > + /* Migration TSC frequency mismatch is fatal only if we are > > + * actually reporting Invariant TSC to the guest. > > */ > > - kvm_arch_set_tsc_khz(cpu); > > + ret = kvm_arch_set_tsc_khz(cpu); > > + if ((x86_cpu->env.features[FEAT_8000_0007_EDX] & CPUID_APM_INVTSC) && > > + ret < 0) { > > + return ret; > > + } > > } > > Will the guest continue in the source in this case? > > I think this is past the point where migration has been declared > successful. > > Otherwise looks good. Good point. I will make additional tests and see if there's some other place where the kvm_arch_set_tsc_khz() call can be moved to.