KVM: PPC: Use exported tb_to_ns() function in decrementer emulation

This changes the KVM code that emulates the decrementer function to do
the conversion of decrementer values to time intervals in nanoseconds
by calling the tb_to_ns() function exported by the powerpc timer code,
in preference to open-coded arithmetic using values from the
decrementer_clockevent struct.  Similarly, the HV-KVM code that did
the same conversion using arithmetic on tb_ticks_per_sec also now
uses tb_to_ns().

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_hv.c

@@ -2160,8 +2160,7 @@ static void kvmppc_set_timer(struct kvm_vcpu *vcpu)
 		kvmppc_core_prepare_to_enter(vcpu);
 		return;
 	}
-	dec_nsec = (vcpu->arch.dec_expires - now) * NSEC_PER_SEC
-		   / tb_ticks_per_sec;
+	dec_nsec = tb_to_ns(vcpu->arch.dec_expires - now);
 	hrtimer_start(&vcpu->arch.dec_timer, dec_nsec, HRTIMER_MODE_REL);
 	vcpu->arch.timer_running = 1;
 }

arch/powerpc/kvm/emulate.c

@@ -61,11 +61,10 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
 
 	dec_time = vcpu->arch.dec;
 	/*
-	 * Guest timebase ticks at the same frequency as host decrementer.
-	 * So use the host decrementer calculations for decrementer emulation.
+	 * Guest timebase ticks at the same frequency as host timebase.
+	 * So use the host timebase calculations for decrementer emulation.
 	 */
-	dec_time = dec_time << decrementer_clockevent.shift;
-	do_div(dec_time, decrementer_clockevent.mult);
+	dec_time = tb_to_ns(dec_time);
 	dec_nsec = do_div(dec_time, NSEC_PER_SEC);
 	hrtimer_start(&vcpu->arch.dec_timer,
 		ktime_set(dec_time, dec_nsec), HRTIMER_MODE_REL);