powerpc/pseries: Implement paravirt qspinlocks for SPLPAR

This implements the generic paravirt qspinlocks using H_PROD and
H_CONFER to kick and wait.

This uses an un-directed yield to any CPU rather than the directed
yield to a pre-empted lock holder that paravirtualised simple
spinlocks use, that requires no kick hcall. This is something that
could be investigated and improved in future.

Performance results can be found in the commit which added queued
spinlocks.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200724131423.1362108-5-npiggin@gmail.com

4 files changed, 105 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
index 339e8533464b..9362c94fe3aa 100644
--- a/arch/powerpc/include/asm/paravirt.h
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -28,6 +28,16 @@ static inline void yield_to_preempted(int cpu, u32 yield_count)
 {
 	plpar_hcall_norets(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);
 }
+
+static inline void prod_cpu(int cpu)
+{
+	plpar_hcall_norets(H_PROD, get_hard_smp_processor_id(cpu));
+}
+
+static inline void yield_to_any(void)
+{
+	plpar_hcall_norets(H_CONFER, -1, 0);
+}
 #else
 static inline bool is_shared_processor(void)
 {
@@ -44,6 +54,19 @@ static inline void yield_to_preempted(int cpu, u32 yield_count)
 {
 	___bad_yield_to_preempted(); /* This would be a bug */
 }
+
+extern void ___bad_yield_to_any(void);
+static inline void yield_to_any(void)
+{
+	___bad_yield_to_any(); /* This would be a bug */
+}
+
+extern void ___bad_prod_cpu(void);
+static inline void prod_cpu(int cpu)
+{
+	___bad_prod_cpu(); /* This would be a bug */
+}
+
 #endif
 
 #define vcpu_is_preempted vcpu_is_preempted
@@ -56,4 +79,9 @@ static inline bool vcpu_is_preempted(int cpu)
 	return false;
 }
 
+static inline bool pv_is_native_spin_unlock(void)
+{
+	return !is_shared_processor();
+}
+
 #endif /* _ASM_POWERPC_PARAVIRT_H */
diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h
index c49e33e24edd..f5066f00a08c 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -3,9 +3,47 @@
 #define _ASM_POWERPC_QSPINLOCK_H
 
 #include <asm-generic/qspinlock_types.h>
+#include <asm/paravirt.h>
 
 #define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __pv_queued_spin_unlock(struct qspinlock *lock);
+
+static __always_inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+{
+	if (!is_shared_processor())
+		native_queued_spin_lock_slowpath(lock, val);
+	else
+		__pv_queued_spin_lock_slowpath(lock, val);
+}
+
+#define queued_spin_unlock queued_spin_unlock
+static inline void queued_spin_unlock(struct qspinlock *lock)
+{
+	if (!is_shared_processor())
+		smp_store_release(&lock->locked, 0);
+	else
+		__pv_queued_spin_unlock(lock);
+}
+
+#else
+extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+#endif
+
+static __always_inline void queued_spin_lock(struct qspinlock *lock)
+{
+	u32 val = 0;
+
+	if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
+		return;
+
+	queued_spin_lock_slowpath(lock, val);
+}
+#define queued_spin_lock queued_spin_lock
+
 #define smp_mb__after_spinlock()   smp_mb()
 
 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
@@ -20,6 +58,34 @@ static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
 }
 #define queued_spin_is_locked queued_spin_is_locked
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define SPIN_THRESHOLD (1<<15) /* not tuned */
+
+static __always_inline void pv_wait(u8 *ptr, u8 val)
+{
+	if (*ptr != val)
+		return;
+	yield_to_any();
+	/*
+	 * We could pass in a CPU here if waiting in the queue and yield to
+	 * the previous CPU in the queue.
+	 */
+}
+
+static __always_inline void pv_kick(int cpu)
+{
+	prod_cpu(cpu);
+}
+
+extern void __pv_init_lock_hash(void);
+
+static inline void pv_spinlocks_init(void)
+{
+	__pv_init_lock_hash();
+}
+
+#endif
+
 #include <asm-generic/qspinlock.h>
 
 #endif /* _ASM_POWERPC_QSPINLOCK_H */
diff --git a/arch/powerpc/include/asm/qspinlock_paravirt.h b/arch/powerpc/include/asm/qspinlock_paravirt.h
new file mode 100644
index 000000000000..6b60e7736a47
--- /dev/null
+++ b/arch/powerpc/include/asm/qspinlock_paravirt.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _ASM_POWERPC_QSPINLOCK_PARAVIRT_H
+#define _ASM_POWERPC_QSPINLOCK_PARAVIRT_H
+
+EXPORT_SYMBOL(__pv_queued_spin_unlock);
+
+#endif /* _ASM_POWERPC_QSPINLOCK_PARAVIRT_H */
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 434615f1d761..6ec72282888d 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -10,5 +10,9 @@
 #include <asm/simple_spinlock.h>
 #endif
 
+#ifndef CONFIG_PARAVIRT_SPINLOCKS
+static inline void pv_spinlocks_init(void) { }
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* __ASM_SPINLOCK_H */