KVM: x86: rewrite handling of scaled TSC for kvmclock

This is the same as before:

    kvm_scale_tsc(tgt_tsc_khz)
        = tgt_tsc_khz * ratio
        = tgt_tsc_khz * user_tsc_khz / tsc_khz   (see set_tsc_khz)
        = user_tsc_khz                           (see kvm_guest_time_update)
        = vcpu->arch.virtual_tsc_khz             (see kvm_set_tsc_khz)

However, computing it through kvm_scale_tsc will make it possible
to include the NTP correction in tgt_tsc_khz.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16bbe6d..01d22b3 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1713,7 +1713,7 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
 
 static int kvm_guest_time_update(struct kvm_vcpu *v)
 {
-       unsigned long flags, this_tsc_khz, tgt_tsc_khz;
+       unsigned long flags, tgt_tsc_khz;
        struct kvm_vcpu_arch *vcpu = &v->arch;
        struct kvm_arch *ka = &v->kvm->arch;
        s64 kernel_ns;
@@ -1739,8 +1739,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 
        /* Keep irq disabled to prevent changes to the clock */
        local_irq_save(flags);
-       this_tsc_khz = __this_cpu_read(cpu_tsc_khz);
-       if (unlikely(this_tsc_khz == 0)) {
+       tgt_tsc_khz = __this_cpu_read(cpu_tsc_khz);
+       if (unlikely(tgt_tsc_khz == 0)) {
                local_irq_restore(flags);
                kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
                return 1;
@@ -1775,13 +1775,14 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
        if (!vcpu->pv_time_enabled)
                return 0;
 
-       if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) {
-               tgt_tsc_khz = kvm_has_tsc_control ?
-                       vcpu->virtual_tsc_khz : this_tsc_khz;
+       if (kvm_has_tsc_control)
+               tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz);
+
+       if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) {
                kvm_get_time_scale(NSEC_PER_SEC / 1000, tgt_tsc_khz,
                                   &vcpu->hv_clock.tsc_shift,
                                   &vcpu->hv_clock.tsc_to_system_mul);
-               vcpu->hw_tsc_khz = this_tsc_khz;
+               vcpu->hw_tsc_khz = tgt_tsc_khz;
        }
 
        /* With all the info we got, fill in the values */