s390/smp: improve setup of possible cpu mask

Since under z/VM we cannot have more than 64 cpus, make sure the
cpu_possible_mask does not contain more bits.
This avoids wasting memory for dynamic per-cpu allocations if
CONFIG_NR_CPUS is larger than 64.

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

arch/s390/Kconfig

@@ -135,7 +135,6 @@ config S390
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UID16 if 32BIT
 	select HAVE_VIRT_CPU_ACCOUNTING
-	select INIT_ALL_POSSIBLE
 	select KTIME_SCALAR if 32BIT
 	select MODULES_USE_ELF_RELA
 	select OLD_SIGACTION

arch/s390/include/asm/smp.h

@@ -31,6 +31,7 @@ extern void smp_yield(void);
 extern void smp_stop_cpu(void);
 extern void smp_cpu_set_polarization(int cpu, int val);
 extern int smp_cpu_get_polarization(int cpu);
+extern void smp_fill_possible_mask(void);
 
 #else /* CONFIG_SMP */
 
@@ -50,6 +51,7 @@ static inline int smp_vcpu_scheduled(int cpu) { return 1; }
 static inline void smp_yield_cpu(int cpu) { }
 static inline void smp_yield(void) { }
 static inline void smp_stop_cpu(void) { }
+static inline void smp_fill_possible_mask(void) { }
 
 #endif /* CONFIG_SMP */
 

arch/s390/kernel/setup.c

@@ -1023,6 +1023,7 @@ void __init setup_arch(char **cmdline_p)
 	setup_vmcoreinfo();
 	setup_lowcore();
 
+	smp_fill_possible_mask();
         cpu_init();
 	s390_init_cpu_topology();
 

arch/s390/kernel/smp.c

@@ -721,18 +721,14 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 	return 0;
 }
 
-static int __init setup_possible_cpus(char *s)
-{
-	int max, cpu;
+static unsigned int setup_possible_cpus __initdata;
 
-	if (kstrtoint(s, 0, &max) < 0)
-		return 0;
-	init_cpu_possible(cpumask_of(0));
-	for (cpu = 1; cpu < max && cpu < nr_cpu_ids; cpu++)
-		set_cpu_possible(cpu, true);
+static int __init _setup_possible_cpus(char *s)
+{
+	get_option(&s, &setup_possible_cpus);
 	return 0;
 }
-early_param("possible_cpus", setup_possible_cpus);
+early_param("possible_cpus", _setup_possible_cpus);
 
 #ifdef CONFIG_HOTPLUG_CPU
 
@@ -775,6 +771,17 @@ void __noreturn cpu_die(void)
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
+void __init smp_fill_possible_mask(void)
+{
+	unsigned int possible, cpu;
+
+	possible = setup_possible_cpus;
+	if (!possible)
+		possible = MACHINE_IS_VM ? 64 : nr_cpu_ids;
+	for (cpu = 0; cpu < possible && cpu < nr_cpu_ids; cpu++)
+		set_cpu_possible(cpu, true);
+}
+
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
 	/* request the 0x1201 emergency signal external interrupt */