kvm/ppc: IRQ disabling cleanup

Simplify the handling of lazy EE by going directly from fully-enabled
to hard-disabled.  This replaces the lazy_irq_pending() check
(including its misplaced kvm_guest_exit() call).

As suggested by Tiejun Chen, move the interrupt disabling into
kvmppc_prepare_to_enter() rather than have each caller do it.  Also
move the IRQ enabling on heavyweight exit into
kvmppc_prepare_to_enter().
Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/include/asm/kvm_ppc.h

@@ -456,6 +456,12 @@ static inline void kvmppc_fix_ee_before_entry(void)
 	trace_hardirqs_on();
 
 #ifdef CONFIG_PPC64
+	/*
+	 * To avoid races, the caller must have gone directly from having
+	 * interrupts fully-enabled to hard-disabled.
+	 */
+	WARN_ON(local_paca->irq_happened != PACA_IRQ_HARD_DIS);
+
 	/* Only need to enable IRQs by hard enabling them after this */
 	local_paca->irq_happened = 0;
 	local_paca->soft_enabled = 1;

arch/powerpc/kvm/book3s_pr.c

@@ -999,14 +999,14 @@ int kvmppc_handle_exit_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		 * and if we really did time things so badly, then we just exit
 		 * again due to a host external interrupt.
 		 */
-		local_irq_disable();
 		s = kvmppc_prepare_to_enter(vcpu);
-		if (s <= 0) {
-			local_irq_enable();
+		if (s <= 0)
 			r = s;
-		} else {
+		else {
+			/* interrupts now hard-disabled */
 			kvmppc_fix_ee_before_entry();
 		}
+
 		kvmppc_handle_lost_ext(vcpu);
 	}
 
@@ -1219,12 +1219,10 @@ static int kvmppc_vcpu_run_pr(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 	 * really did time things so badly, then we just exit again due to
 	 * a host external interrupt.
 	 */
-	local_irq_disable();
 	ret = kvmppc_prepare_to_enter(vcpu);
-	if (ret <= 0) {
-		local_irq_enable();
+	if (ret <= 0)
 		goto out;
-	}
+	/* interrupts now hard-disabled */
 
 	/* Save FPU state in thread_struct */
 	if (current->thread.regs->msr & MSR_FP)

arch/powerpc/kvm/booke.c

@@ -643,7 +643,7 @@ int kvmppc_core_prepare_to_enter(struct kvm_vcpu *vcpu)
 		local_irq_enable();
 		kvm_vcpu_block(vcpu);
 		clear_bit(KVM_REQ_UNHALT, &vcpu->requests);
-		local_irq_disable();
+		hard_irq_disable();
 
 		kvmppc_set_exit_type(vcpu, EMULATED_MTMSRWE_EXITS);
 		r = 1;
@@ -688,13 +688,12 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 		return -EINVAL;
 	}
 
-	local_irq_disable();
 	s = kvmppc_prepare_to_enter(vcpu);
 	if (s <= 0) {
-		local_irq_enable();
 		ret = s;
 		goto out;
 	}
+	/* interrupts now hard-disabled */
 
 #ifdef CONFIG_PPC_FPU
 	/* Save userspace FPU state in stack */
@@ -1187,12 +1186,11 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 * aren't already exiting to userspace for some other reason.
 	 */
 	if (!(r & RESUME_HOST)) {
-		local_irq_disable();
 		s = kvmppc_prepare_to_enter(vcpu);
-		if (s <= 0) {
-			local_irq_enable();
+		if (s <= 0)
 			r = (s << 2) | RESUME_HOST | (r & RESUME_FLAG_NV);
-		} else {
+		else {
+			/* interrupts now hard-disabled */
 			kvmppc_fix_ee_before_entry();
 		}
 	}

arch/powerpc/kvm/powerpc.c

@@ -68,14 +68,16 @@ int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
  */
 int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 {
-	int r = 1;
+	int r;
+
+	WARN_ON(irqs_disabled());
+	hard_irq_disable();
 
-	WARN_ON_ONCE(!irqs_disabled());
 	while (true) {
 		if (need_resched()) {
 			local_irq_enable();
 			cond_resched();
-			local_irq_disable();
+			hard_irq_disable();
 			continue;
 		}
 
@@ -101,7 +103,7 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			local_irq_enable();
 			trace_kvm_check_requests(vcpu);
 			r = kvmppc_core_check_requests(vcpu);
-			local_irq_disable();
+			hard_irq_disable();
 			if (r > 0)
 				continue;
 			break;
@@ -113,22 +115,12 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			continue;
 		}
 
-#ifdef CONFIG_PPC64
-		/* lazy EE magic */
-		hard_irq_disable();
-		if (lazy_irq_pending()) {
-			/* Got an interrupt in between, try again */
-			local_irq_enable();
-			local_irq_disable();
-			kvm_guest_exit();
-			continue;
-		}
-#endif
-
 		kvm_guest_enter();
-		break;
+		return 1;
 	}
 
+	/* return to host */
+	local_irq_enable();
 	return r;
 }
 EXPORT_SYMBOL_GPL(kvmppc_prepare_to_enter);