[kvm-unit-tests PATCH v5 27/29] powerpc: Avoid using larx/stcx. in spinlocks when only one CPU is running

[Nicholas Piggin <npiggin@xxxxxxxxx>]

The test harness uses spinlocks if they are implemented with larx/stcx.
it can prevent some test scenarios such as testing migration of a
reservation.

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
 lib/powerpc/asm/smp.h    |  1 +
 lib/powerpc/smp.c        |  6 ++++++
 lib/powerpc/spinlock.c   | 28 ++++++++++++++++++++++++++++
 lib/ppc64/asm/spinlock.h |  7 ++++++-
 powerpc/Makefile.common  |  1 +
 5 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 lib/powerpc/spinlock.c

diff --git a/lib/powerpc/asm/smp.h b/lib/powerpc/asm/smp.h
index 163bbeec..e2c03295 100644
--- a/lib/powerpc/asm/smp.h
+++ b/lib/powerpc/asm/smp.h
@@ -19,5 +19,6 @@ void local_ipi_disable(void);
 void send_ipi(int cpu_id);
 
 extern int nr_cpus_online;
+extern bool multithreaded;
 
 #endif /* _ASMPOWERPC_SMP_H_ */
diff --git a/lib/powerpc/smp.c b/lib/powerpc/smp.c
index 96e3219a..b473ba41 100644
--- a/lib/powerpc/smp.c
+++ b/lib/powerpc/smp.c
@@ -280,6 +280,8 @@ static void start_each_secondary(int fdtnode, u64 regval __unused, void *info)
 	datap->nr_started += start_core(fdtnode, datap->entry);
 }
 
+bool multithreaded = false;
+
 /*
  * Start all stopped cpus on the guest at entry with register 3 set to r3
  * We expect that we come in with only one thread currently started
@@ -293,8 +295,10 @@ bool start_all_cpus(secondary_entry_fn entry)
 
 	memset(start_secondary_cpus, 0xff, sizeof(start_secondary_cpus));
 
+	assert(!multithreaded);
 	assert(nr_cpus_online == 1);
 
+	multithreaded = true;
 	nr_started = 0;
 	nr_cpus_present = 0;
 	ret = dt_for_each_cpu_node(start_each_secondary, &data);
@@ -305,6 +309,8 @@ bool start_all_cpus(secondary_entry_fn entry)
 
 void stop_all_cpus(void)
 {
+	assert(multithreaded);
 	while (nr_cpus_online > 1)
 		cpu_relax();
+	multithreaded = false;
 }
diff --git a/lib/powerpc/spinlock.c b/lib/powerpc/spinlock.c
new file mode 100644
index 00000000..238549f1
--- /dev/null
+++ b/lib/powerpc/spinlock.c
@@ -0,0 +1,28 @@
+#include <asm/spinlock.h>
+#include <asm/smp.h>
+
+/*
+ * Skip the atomic when single-threaded, which helps avoid larx/stcx. in
+ * the harness when testing tricky larx/stcx. sequences (e.g., migration
+ * vs reservation).
+ */
+void spin_lock(struct spinlock *lock)
+{
+	if (!multithreaded) {
+		assert(lock->v == 0);
+		lock->v = 1;
+	} else {
+		while (__sync_lock_test_and_set(&lock->v, 1))
+			;
+	}
+}
+
+void spin_unlock(struct spinlock *lock)
+{
+	assert(lock->v == 1);
+	if (!multithreaded) {
+		lock->v = 0;
+	} else {
+		__sync_lock_release(&lock->v);
+	}
+}
diff --git a/lib/ppc64/asm/spinlock.h b/lib/ppc64/asm/spinlock.h
index f59eed19..b952386d 100644
--- a/lib/ppc64/asm/spinlock.h
+++ b/lib/ppc64/asm/spinlock.h
@@ -1,6 +1,11 @@
 #ifndef _ASMPPC64_SPINLOCK_H_
 #define _ASMPPC64_SPINLOCK_H_
 
-#include <asm-generic/spinlock.h>
+struct spinlock {
+	unsigned int v;
+};
+
+void spin_lock(struct spinlock *lock);
+void spin_unlock(struct spinlock *lock);
 
 #endif /* _ASMPPC64_SPINLOCK_H_ */
diff --git a/powerpc/Makefile.common b/powerpc/Makefile.common
index f9dd937a..caa807f2 100644
--- a/powerpc/Makefile.common
+++ b/powerpc/Makefile.common
@@ -47,6 +47,7 @@ cflatobjs += lib/powerpc/rtas.o
 cflatobjs += lib/powerpc/processor.o
 cflatobjs += lib/powerpc/handlers.o
 cflatobjs += lib/powerpc/smp.o
+cflatobjs += lib/powerpc/spinlock.o
 
 OBJDIRS += lib/powerpc
 
-- 
2.42.0