[S390] spinlock: check virtual cpu running status

This patch introduces a new function that checks the running status
of a cpu in a hypervisor. This status is not virtualized, so the check
is only correct if running in an LPAR. On acquiring a spinlock, if the
cpu holding the lock is scheduled by the hypervisor, we do a busy wait
on the lock. If it is not scheduled, we yield over to that cpu.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/s390/include/asm/smp.h b/arch/s390/include/asm/smp.h
index c2d0e638f892..edc03cb9cd79 100644
--- a/arch/s390/include/asm/smp.h
+++ b/arch/s390/include/asm/smp.h
@@ -36,6 +36,28 @@ extern void smp_switch_to_cpu(void (*)(void *), void *, unsigned long sp,
                               int from, int to);
 extern void smp_restart_cpu(void);
 
+/*
+ * returns 1 if (virtual) cpu is scheduled
+ * returns 0 otherwise
+ */
+static inline int smp_vcpu_scheduled(int cpu)
+{
+        u32 status;
+
+        switch (sigp_ps(&status, 0, cpu, sigp_sense_running)) {
+        case sigp_status_stored:
+                /* Check for running status */
+                if (status & 0x400)
+                        return 0;
+                break;
+        case sigp_not_operational:
+                return 0;
+        default:
+                break;
+        }
+        return 1;
+}
+
 #else /* CONFIG_SMP */
 
 static inline void smp_switch_to_ipl_cpu(void (*func)(void *), void *data)
@@ -43,6 +65,8 @@ static inline void smp_switch_to_ipl_cpu(void (*func)(void *), void *data)
         func(data);
 }
 
+#define smp_vcpu_scheduled      (1)
+
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_HOTPLUG_CPU