KVM: Don't update PPR on any APIC read

The current code will update the PPR on almost any APIC read; however
that's only required if we read the PPR.

kvm_update_ppr() shows up in some profiles, albeit with a low usage (~1%).
This should reduce it further (it will still be called during interrupt
processing).
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/lapic.c

@@ -696,12 +696,14 @@ static u32 __apic_read(struct kvm_lapic *apic, unsigned int offset)
 
 		val = apic_get_tmcct(apic);
 		break;
-
+	case APIC_PROCPRI:
+		apic_update_ppr(apic);
+		val = apic_get_reg(apic, offset);
+		break;
 	case APIC_TASKPRI:
 		report_tpr_access(apic, false);
 		/* fall thru */
 	default:
-		apic_update_ppr(apic);
 		val = apic_get_reg(apic, offset);
 		break;
 	}