[S390] Limit cpu detection to 256 physical cpus.

Saves us more than 65k pointless IPIs.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/cpu.h

@@ -0,0 +1,6 @@
+#ifndef _ASM_S390_CPU_H
+#define _ASM_S390_CPU_H
+
+#define MAX_CPU_ADDRESS 255
+
+#endif /* _ASM_S390_CPU_H */

arch/s390/kernel/head.S

@@ -27,6 +27,7 @@
 #include <asm/asm-offsets.h>
 #include <asm/thread_info.h>
 #include <asm/page.h>
+#include <asm/cpu.h>
 
 #ifdef CONFIG_64BIT
 #define ARCH_OFFSET	4

arch/s390/kernel/head64.S

@@ -62,9 +62,9 @@ startup_continue:
 	clr	%r11,%r12
 	je	5f			# no more space in prefix array
 4:
-	ahi	%r8,1				# next cpu (r8 += 1)
-	cl	%r8,.Llast_cpu-.LPG1(%r13)	# is last possible cpu ?
-	jl	1b				# jump if not last cpu
+	ahi	%r8,1			# next cpu (r8 += 1)
+	chi	%r8,MAX_CPU_ADDRESS	# is last possible cpu ?
+	jle	1b			# jump if not last cpu
 5:
 	lhi	%r1,2			# mode 2 = esame (dump)
 	j	6f
@@ -130,8 +130,6 @@ startup_continue:
 #ifdef CONFIG_ZFCPDUMP
 .Lcurrent_cpu:
 	.long 0x0
-.Llast_cpu:
-	.long 0x0000ffff
 .Lpref_arr_ptr:
 	.long zfcpdump_prefix_array
 #endif /* CONFIG_ZFCPDUMP */

arch/s390/kernel/smp.c

@@ -49,6 +49,7 @@
 #include <asm/sclp.h>
 #include <asm/cputime.h>
 #include <asm/vdso.h>
+#include <asm/cpu.h>
 #include "entry.h"
 
 static struct task_struct *current_set[NR_CPUS];
@@ -300,7 +301,7 @@ static int smp_rescan_cpus_sigp(cpumask_t avail)
 	logical_cpu = cpumask_first(&avail);
 	if (logical_cpu >= nr_cpu_ids)
 		return 0;
-	for (cpu_id = 0; cpu_id <= 65535; cpu_id++) {
+	for (cpu_id = 0; cpu_id <= MAX_CPU_ADDRESS; cpu_id++) {
 		if (cpu_known(cpu_id))
 			continue;
 		__cpu_logical_map[logical_cpu] = cpu_id;
@@ -379,7 +380,7 @@ static void __init smp_detect_cpus(void)
 	/* Use sigp detection algorithm if sclp doesn't work. */
 	if (sclp_get_cpu_info(info)) {
 		smp_use_sigp_detection = 1;
-		for (cpu = 0; cpu <= 65535; cpu++) {
+		for (cpu = 0; cpu <= MAX_CPU_ADDRESS; cpu++) {
 			if (cpu == boot_cpu_addr)
 				continue;
 			__cpu_logical_map[CPU_INIT_NO] = cpu;