Going through the first VCPU is wrong if you follow a KVM_SET_CLOCK with
a KVM_GET_CLOCK immediately after, without letting the VCPU run and
call kvm_guest_time_update.
To fix this, compute the kvmclock value ourselves, using the master
clock (tsc, nsec) pair as the base and the host CPU frequency as
the scale.
Reported-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1ba08278a9a9..c4b07d6f7bf1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1620,6 +1620,11 @@ static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
}
+#else
+static inline bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
+{
+ return false;
+}
#endif
/*
@@ -1724,18 +1729,18 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
static u64 __get_kvmclock_ns(struct kvm *kvm)
{
- struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, 0);
struct kvm_arch *ka = &kvm->arch;
- s64 ns;
+ struct pvclock_vcpu_time_info hv_clock;
- if (vcpu->arch.hv_clock.flags & PVCLOCK_TSC_STABLE_BIT) {
- u64 tsc = kvm_read_l1_tsc(vcpu, rdtsc());
- ns = __pvclock_read_cycles(&vcpu->arch.hv_clock, tsc);
- } else {
- ns = ktime_get_boot_ns() + ka->kvmclock_offset;
- }
+ if (!ka->use_master_clock)
+ return ktime_get_boot_ns() + ka->kvmclock_offset;
- return ns;
+ hv_clock.tsc_timestamp = ka->master_cycle_now;
+ hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
+ kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
+ &hv_clock.tsc_shift,
+ &hv_clock.tsc_to_system_mul);
+ return __pvclock_read_cycles(&hv_clock, rdtsc());
}
u64 get_kvmclock_ns(struct kvm *kvm)
--
1.8.3.1
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