KVM: PPC: Book3S HV: Ratelimit machine check messages coming from guests

A number of machine check exceptions are triggerable by the guest.
Ratelimit these to avoid a guest flooding the host console and logs.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Use dedicated ratelimit state, not printk_ratelimit()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201128070728.825934-5-npiggin@gmail.com

arch/powerpc/kvm/book3s_hv.c

@@ -1327,9 +1327,15 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 	case BOOK3S_INTERRUPT_SYSTEM_RESET:
 		r = RESUME_GUEST;
 		break;
-	case BOOK3S_INTERRUPT_MACHINE_CHECK:
-		/* Print the MCE event to host console. */
-		machine_check_print_event_info(&vcpu->arch.mce_evt, false, true);
+	case BOOK3S_INTERRUPT_MACHINE_CHECK: {
+		static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+					      DEFAULT_RATELIMIT_BURST);
+		/*
+		 * Print the MCE event to host console. Ratelimit so the guest
+		 * can't flood the host log.
+		 */
+		if (__ratelimit(&rs))
+			machine_check_print_event_info(&vcpu->arch.mce_evt,false, true);
 
 		/*
 		 * If the guest can do FWNMI, exit to userspace so it can
@@ -1357,6 +1363,7 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 
 		r = RESUME_HOST;
 		break;
+	}
 	case BOOK3S_INTERRUPT_PROGRAM:
 	{
 		ulong flags;
@@ -1516,11 +1523,16 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu *vcpu)
 		r = RESUME_GUEST;
 		break;
 	case BOOK3S_INTERRUPT_MACHINE_CHECK:
+	{
+		static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+					      DEFAULT_RATELIMIT_BURST);
 		/* Pass the machine check to the L1 guest */
 		r = RESUME_HOST;
 		/* Print the MCE event to host console. */
-		machine_check_print_event_info(&vcpu->arch.mce_evt, false, true);
+		if (__ratelimit(&rs))
+			machine_check_print_event_info(&vcpu->arch.mce_evt, false, true);
 		break;
+	}
 	/*
 	 * We get these next two if the guest accesses a page which it thinks
 	 * it has mapped but which is not actually present, either because