diff --git a/lib/s390x/asm/interrupt.h b/lib/s390x/asm/interrupt.h
index 013709f..f485e96 100644
--- a/lib/s390x/asm/interrupt.h
+++ b/lib/s390x/asm/interrupt.h
@@ -11,6 +11,8 @@
 #define _ASMS390X_IRQ_H_
 #include <asm/arch_def.h>
 
+#define EXT_IRQ_SERVICE_SIG	0x2401
+
 void handle_pgm_int(void);
 void handle_ext_int(void);
 void handle_mcck_int(void);
diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
index cf0a794..7832711 100644
--- a/lib/s390x/interrupt.c
+++ b/lib/s390x/interrupt.c
@@ -12,6 +12,7 @@
 #include <libcflat.h>
 #include <asm/interrupt.h>
 #include <asm/barrier.h>
+#include <sclp.h>
 
 static bool pgm_int_expected;
 static struct lowcore *lc;
@@ -107,8 +108,15 @@ void handle_pgm_int(void)
 
 void handle_ext_int(void)
 {
-	report_abort("Unexpected external call interrupt: at %#lx",
-		     lc->ext_old_psw.addr);
+	if (lc->ext_int_code != EXT_IRQ_SERVICE_SIG) {
+		report_abort("Unexpected external call interrupt: at %#lx",
+			     lc->ext_old_psw.addr);
+	} else {
+		lc->ext_old_psw.mask &= ~PSW_MASK_EXT;
+		lc->sw_int_cr0 &= ~(1UL << 9);
+		sclp_handle_ext();
+		lc->ext_int_code = 0;
+	}
 }
 
 void handle_mcck_int(void)
diff --git a/lib/s390x/sclp-console.c b/lib/s390x/sclp-console.c
index bc01f41..a5ef45f 100644
--- a/lib/s390x/sclp-console.c
+++ b/lib/s390x/sclp-console.c
@@ -17,6 +17,7 @@ static void sclp_set_write_mask(void)
 {
 	WriteEventMask *sccb = (void *)_sccb;
 
+	sclp_mark_busy();
 	sccb->h.length = sizeof(WriteEventMask);
 	sccb->mask_length = sizeof(unsigned int);
 	sccb->receive_mask = SCLP_EVENT_MASK_MSG_ASCII;
@@ -37,6 +38,7 @@ void sclp_print(const char *str)
 	int len = strlen(str);
 	WriteEventData *sccb = (void *)_sccb;
 
+	sclp_mark_busy();
 	sccb->h.length = sizeof(WriteEventData) + len;
 	sccb->h.function_code = SCLP_FC_NORMAL_WRITE;
 	sccb->ebh.length = sizeof(EventBufferHeader) + len;
diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
index b60f7a4..257eb02 100644
--- a/lib/s390x/sclp.c
+++ b/lib/s390x/sclp.c
@@ -14,6 +14,8 @@
 #include <asm/page.h>
 #include <asm/arch_def.h>
 #include <asm/interrupt.h>
+#include <asm/barrier.h>
+#include <asm/spinlock.h>
 #include "sclp.h"
 #include <alloc_phys.h>
 #include <alloc_page.h>
@@ -25,6 +27,8 @@ static uint64_t max_ram_size;
 static uint64_t ram_size;
 
 char _sccb[PAGE_SIZE] __attribute__((__aligned__(4096)));
+static volatile bool sclp_busy;
+static struct spinlock sclp_lock;
 
 static void mem_init(phys_addr_t mem_end)
 {
@@ -41,17 +45,61 @@ static void mem_init(phys_addr_t mem_end)
 	page_alloc_ops_enable();
 }
 
+static void sclp_setup_int(void)
+{
+	uint64_t mask;
+
+	ctl_set_bit(0, 9);
+
+	mask = extract_psw_mask();
+	mask |= PSW_MASK_EXT;
+	load_psw_mask(mask);
+}
+
+void sclp_handle_ext(void)
+{
+	ctl_clear_bit(0, 9);
+	spin_lock(&sclp_lock);
+	sclp_busy = false;
+	spin_unlock(&sclp_lock);
+}
+
+void sclp_wait_busy(void)
+{
+	while (sclp_busy)
+		mb();
+}
+
+void sclp_mark_busy(void)
+{
+	/*
+	 * With multiple CPUs we might need to wait for another CPU's
+	 * request before grabbing the busy indication.
+	 */
+retry_wait:
+	sclp_wait_busy();
+	spin_lock(&sclp_lock);
+	if (sclp_busy) {
+		spin_unlock(&sclp_lock);
+		goto retry_wait;
+	}
+	sclp_busy = true;
+	spin_unlock(&sclp_lock);
+}
+
 static void sclp_read_scp_info(ReadInfo *ri, int length)
 {
 	unsigned int commands[] = { SCLP_CMDW_READ_SCP_INFO_FORCED,
 				    SCLP_CMDW_READ_SCP_INFO };
-	int i;
+	int i, cc;
 
 	for (i = 0; i < ARRAY_SIZE(commands); i++) {
+		sclp_mark_busy();
 		memset(&ri->h, 0, sizeof(ri->h));
 		ri->h.length = length;
 
-		if (sclp_service_call(commands[i], ri))
+		cc = sclp_service_call(commands[i], ri);
+		if (cc)
 			break;
 		if (ri->h.response_code == SCLP_RC_NORMAL_READ_COMPLETION)
 			return;
@@ -66,12 +114,14 @@ int sclp_service_call(unsigned int command, void *sccb)
 {
 	int cc;
 
+	sclp_setup_int();
 	asm volatile(
 		"       .insn   rre,0xb2200000,%1,%2\n"  /* servc %1,%2 */
 		"       ipm     %0\n"
 		"       srl     %0,28"
 		: "=&d" (cc) : "d" (command), "a" (__pa(sccb))
 		: "cc", "memory");
+	sclp_wait_busy();
 	if (cc == 3)
 		return -1;
 	if (cc == 2)
diff --git a/lib/s390x/sclp.h b/lib/s390x/sclp.h
index 583c4e5..63cf609 100644
--- a/lib/s390x/sclp.h
+++ b/lib/s390x/sclp.h
@@ -213,6 +213,9 @@ typedef struct ReadEventData {
 } __attribute__((packed)) ReadEventData;
 
 extern char _sccb[];
+void sclp_handle_ext(void);
+void sclp_wait_busy(void);
+void sclp_mark_busy(void);
 void sclp_console_setup(void);
 void sclp_print(const char *str);
 int sclp_service_call(unsigned int command, void *sccb);
