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>

3 files changed, 26 insertions, 6 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);
 }
diff --git a/drivers/s390/char/sclp_early.c b/drivers/s390/char/sclp_early.c
index 2c6aac66e2b0..14196ea0fdf3 100644
--- a/drivers/s390/char/sclp_early.c
+++ b/drivers/s390/char/sclp_early.c
@@ -20,7 +20,9 @@ struct read_info_sccb {
         struct  sccb_header header;     /* 0-7 */
         u16     rnmax;                  /* 8-9 */
         u8      rnsize;                 /* 10 */
-        u8      _reserved0[24 - 11];    /* 11-15 */
+        u8      _reserved0[16 - 11];    /* 11-15 */
+        u16     ncpurl;                 /* 16-17 */
+        u8      _reserved7[24 - 18];    /* 18-23 */
         u8      loadparm[8];            /* 24-31 */
         u8      _reserved1[48 - 32];    /* 32-47 */
         u64     facilities;             /* 48-55 */
@@ -32,13 +34,16 @@ struct read_info_sccb {
         u8      _reserved4[100 - 92];   /* 92-99 */
         u32     rnsize2;                /* 100-103 */
         u64     rnmax2;                 /* 104-111 */
-        u8      _reserved5[4096 - 112]; /* 112-4095 */
+        u8      _reserved5[120 - 112];  /* 112-119 */
+        u16     hcpua;                  /* 120-121 */
+        u8      _reserved6[4096 - 122]; /* 122-4095 */
 } __packed __aligned(PAGE_SIZE);
 
 static char sccb_early[PAGE_SIZE] __aligned(PAGE_SIZE) __initdata;
 static unsigned int sclp_con_has_vt220 __initdata;
 static unsigned int sclp_con_has_linemode __initdata;
 static unsigned long sclp_hsa_size;
+static unsigned int sclp_max_cpu;
 static struct sclp_ipl_info sclp_ipl_info;
 
 u64 sclp_facilities;
@@ -102,6 +107,15 @@ static void __init sclp_facilities_detect(struct read_info_sccb *sccb)
         sclp_rzm = sccb->rnsize ? sccb->rnsize : sccb->rnsize2;
         sclp_rzm <<= 20;
 
+        if (!sccb->hcpua) {
+                if (MACHINE_IS_VM)
+                        sclp_max_cpu = 64;
+                else
+                        sclp_max_cpu = sccb->ncpurl;
+        } else {
+                sclp_max_cpu = sccb->hcpua + 1;
+        }
+
         /* Save IPL information */
         sclp_ipl_info.is_valid = 1;
         if (sccb->flags & 0x2)
@@ -129,6 +143,11 @@ unsigned long long sclp_get_rzm(void)
         return sclp_rzm;
 }
 
+unsigned int sclp_get_max_cpu(void)
+{
+        return sclp_max_cpu;
+}
+
 /*
  * This function will be called after sclp_facilities_detect(), which gets
  * called from early.c code. The sclp_facilities_detect() function retrieves