s390/smp: limit number of cpus in possible cpu mask

Limit the number of bits to the maximum number of cpus a machine
can have.
possible_cpu_mask typically will have more bits set than a machine
may physically have. This results in wasted memory during per-cpu
memory allocations, if the possible mask contains more cpus than
physically possible for a given configuration.

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

2 files changed, 5 insertions, 4 deletions

diff --git a/arch/s390/include/asm/sclp.h b/arch/s390/include/asm/sclp.h
index abaca2275c7a..2f5e9932b4de 100644
--- a/arch/s390/include/asm/sclp.h
+++ b/arch/s390/include/asm/sclp.h
@@ -46,6 +46,7 @@ int sclp_cpu_configure(u8 cpu);
 int sclp_cpu_deconfigure(u8 cpu);
 unsigned long long sclp_get_rnmax(void);
 unsigned long long sclp_get_rzm(void);
+unsigned int sclp_get_max_cpu(void);
 int sclp_sdias_blk_count(void);
 int sclp_sdias_copy(void *dest, int blk_num, int nr_blks);
 int sclp_chp_configure(struct chp_id chpid);
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index a7125b62a9a6..8827883310dd 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -773,11 +773,11 @@ void __noreturn cpu_die(void)
 
 void __init smp_fill_possible_mask(void)
 {
-        unsigned int possible, cpu;
+        unsigned int possible, sclp, cpu;
 
-        possible = setup_possible_cpus;
-        if (!possible)
-                possible = MACHINE_IS_VM ? 64 : nr_cpu_ids;
+        sclp = sclp_get_max_cpu() ?: nr_cpu_ids;
+        possible = setup_possible_cpus ?: nr_cpu_ids;
+        possible = min(possible, sclp);
         for (cpu = 0; cpu < possible && cpu < nr_cpu_ids; cpu++)
                 set_cpu_possible(cpu, true);
 }