[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>

3 files changed, 80 insertions, 37 deletions

diff --git a/arch/s390/include/asm/sigp.h b/arch/s390/include/asm/sigp.h
index 8aa46ce4229c..e3bffd4e2d66 100644
--- a/arch/s390/include/asm/sigp.h
+++ b/arch/s390/include/asm/sigp.h
@@ -25,29 +25,28 @@ static inline int cpu_logical_map(int cpu)
 }
 
 enum {
-        sigp_unassigned=0x0,
-        sigp_sense,
-        sigp_external_call,
-        sigp_emergency_signal,
-        sigp_start,
-        sigp_stop,
-        sigp_restart,
-        sigp_unassigned1,
-        sigp_unassigned2,
-        sigp_stop_and_store_status,
-        sigp_unassigned3,
-        sigp_initial_cpu_reset,
-        sigp_cpu_reset,
-        sigp_set_prefix,
-        sigp_store_status_at_address,
-        sigp_store_extended_status_at_address
+        sigp_sense = 1,
+        sigp_external_call = 2,
+        sigp_emergency_signal = 3,
+        sigp_start = 4,
+        sigp_stop = 5,
+        sigp_restart = 6,
+        sigp_stop_and_store_status = 9,
+        sigp_initial_cpu_reset = 11,
+        sigp_cpu_reset = 12,
+        sigp_set_prefix = 13,
+        sigp_store_status_at_address = 14,
+        sigp_store_extended_status_at_address = 15,
+        sigp_set_architecture = 18,
+        sigp_conditional_emergency_signal = 19,
+        sigp_sense_running = 21,
 };
 
 enum {
-        sigp_order_code_accepted=0,
-        sigp_status_stored,
-        sigp_busy,
-        sigp_not_operational
+        sigp_order_code_accepted = 0,
+        sigp_status_stored = 1,
+        sigp_busy = 2,
+        sigp_not_operational = 3,
 };
 
 /*
@@ -57,7 +56,6 @@ enum {
         ec_schedule = 0,
         ec_call_function,
         ec_call_function_single,
-        ec_bit_last
 };
 
 /*
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
diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index cff327f109a8..91754ffb9203 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -43,16 +43,24 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
 {
         int count = spin_retry;
         unsigned int cpu = ~smp_processor_id();
+        unsigned int owner;
 
         while (1) {
-                if (count-- <= 0) {
-                        unsigned int owner = lp->owner_cpu;
-                        if (owner != 0)
-                                _raw_yield_cpu(~owner);
-                        count = spin_retry;
+                owner = lp->owner_cpu;
+                if (!owner || smp_vcpu_scheduled(~owner)) {
+                        for (count = spin_retry; count > 0; count--) {
+                                if (arch_spin_is_locked(lp))
+                                        continue;
+                                if (_raw_compare_and_swap(&lp->owner_cpu, 0,
+                                                          cpu) == 0)
+                                        return;
+                        }
+                        if (MACHINE_IS_LPAR)
+                                continue;
                 }
-                if (arch_spin_is_locked(lp))
-                        continue;
+                owner = lp->owner_cpu;
+                if (owner)
+                        _raw_yield_cpu(~owner);
                 if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
                         return;
         }
@@ -63,17 +71,27 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
 {
         int count = spin_retry;
         unsigned int cpu = ~smp_processor_id();
+        unsigned int owner;
 
         local_irq_restore(flags);
         while (1) {
-                if (count-- <= 0) {
-                        unsigned int owner = lp->owner_cpu;
-                        if (owner != 0)
-                                _raw_yield_cpu(~owner);
-                        count = spin_retry;
+                owner = lp->owner_cpu;
+                if (!owner || smp_vcpu_scheduled(~owner)) {
+                        for (count = spin_retry; count > 0; count--) {
+                                if (arch_spin_is_locked(lp))
+                                        continue;
+                                local_irq_disable();
+                                if (_raw_compare_and_swap(&lp->owner_cpu, 0,
+                                                          cpu) == 0)
+                                        return;
+                                local_irq_restore(flags);
+                        }
+                        if (MACHINE_IS_LPAR)
+                                continue;
                 }
-                if (arch_spin_is_locked(lp))
-                        continue;
+                owner = lp->owner_cpu;
+                if (owner)
+                        _raw_yield_cpu(~owner);
                 local_irq_disable();
                 if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
                         return;
@@ -100,8 +118,11 @@ EXPORT_SYMBOL(arch_spin_trylock_retry);
 void arch_spin_relax(arch_spinlock_t *lock)
 {
         unsigned int cpu = lock->owner_cpu;
-        if (cpu != 0)
-                _raw_yield_cpu(~cpu);
+        if (cpu != 0) {
+                if (MACHINE_IS_VM || MACHINE_IS_KVM ||
+                    !smp_vcpu_scheduled(~cpu))
+                        _raw_yield_cpu(~cpu);
+        }
 }
 EXPORT_SYMBOL(arch_spin_relax);