On Fri, Sep 29, 2023, Woodhouse, David wrote: > Poking around at various places which calculate the time "now" in some > clock domain... then maybe get preempted for a while... and then > compare that with the time "now" in the same or another clock domain. > > This one with its "ktime_get_real_ns() - get_kvmclock_ns(kvm);" seemed > like perfect low-hanging fruit to start with. ... > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 04b57a336b34..0ec989bb61a1 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2317,14 +2317,9 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock, int sec_hi_o > if (kvm_write_guest(kvm, wall_clock, &version, sizeof(version))) > return; > > - /* > - * The guest calculates current wall clock time by adding > - * system time (updated by kvm_guest_time_update below) to the > - * wall clock specified here. We do the reverse here. > - */ > - wall_nsec = ktime_get_real_ns() - get_kvmclock_ns(kvm); > + wall_nsec = kvm_get_wall_clock_epoch(kvm); Possibly silly question: why can't preemption simply be disabled for the duration of the sensitive calculation?
