[kvm-unit-tests PATCH v8 24/35] powerpc: Avoid using larx/stcx. in spinlocks when only one CPU is running

Nicholas Piggin
2024-04-05T08:37:28Z

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@gmail.com>
---
lib/powerpc/asm/smp.h | 1 +
lib/powerpc/smp.c | 5 +++++
lib/powerpc/spinlock.c | 29 +++++++++++++++++++++++++++++
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 4519e5436..6ef3ae521 100644
--- a/lib/powerpc/asm/smp.h
+++ b/lib/powerpc/asm/smp.h
@@ -15,6 +15,7 @@ struct cpu {

extern int nr_cpus_present;
extern int nr_cpus_online;
+extern bool multithreaded;
extern struct cpu cpus[];

register struct cpu *__current_cpu asm("r13");
diff --git a/lib/powerpc/smp.c b/lib/powerpc/smp.c
index a3bf85d44..f3b2a3faf 100644
--- a/lib/powerpc/smp.c
+++ b/lib/powerpc/smp.c
@@ -276,6 +276,8 @@ static void start_each_secondary(int fdtnode, u64 regval __unused, void *info)
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
@@ -290,6 +292,7 @@ bool start_all_cpus(secondary_entry_fn entry)

assert(nr_cpus_online == 1);
assert(nr_started == 1);
+ multithreaded = true;
ret = dt_for_each_cpu_node(start_each_secondary, &data);
assert(ret == 0);
assert(nr_started == nr_cpus_present);
@@ -308,8 +311,10 @@ bool start_all_cpus(secondary_entry_fn entry)

void stop_all_cpus(void)
{
+ assert(multithreaded);
while (nr_cpus_online > 1)
cpu_relax();
mb();
nr_started = 1;
+ multithreaded = false;
}
diff --git a/lib/powerpc/spinlock.c b/lib/powerpc/spinlock.c
new file mode 100644
index 000000000..623a1f2c1
--- /dev/null
+++ b/lib/powerpc/spinlock.c
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: LGPL-2.0 */
+#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 f59eed191..b952386da 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 744dfc1f7..02af54b83 100644
--- a/powerpc/Makefile.common
+++ b/powerpc/Makefile.common
@@ -48,6 +48,7 @@ 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

--
2.43.0