[PATCH v2] KVM: arm64: Fix hyp_trace clock disabling

[Vincent Donnefort]

Fix the disable path in hyp_trace_clock_enable(), which fell through to
re-initialize and reschedule the clock after cancelling the work. Return
early instead.

While at it, cleanup hyp_trace_clock::lock which is unused and
hyp_trace_clock::running which is redundant: the trace_remote framework
already serializes calls to the callback enable_tracing.

Fixes: b22888917fa4 ("KVM: arm64: Sync boot clock with the nVHE/pKVM hyp")
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

--- 

v1 -> v2:
  * Rollback hyp_trace_clock_enable() on __tracing_enable error (Sashiko)

v1: https://lore.kernel.org/all/alczBmnItMwq8xj4@google.com/

diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 2411b4c32932..9bfa368dd841 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -37,8 +37,6 @@ static struct hyp_trace_clock {
 	u32			shift;
 	struct delayed_work	work;
 	struct completion	ready;
-	struct mutex		lock;
-	bool			running;
 } hyp_clock;
 
 static void __hyp_clock_work(struct work_struct *work)
@@ -110,12 +108,9 @@ static void hyp_trace_clock_enable(struct hyp_trace_clock *hyp_clock, bool enabl
 {
 	struct system_time_snapshot snap;
 
-	if (hyp_clock->running == enable)
-		return;
-
 	if (!enable) {
 		cancel_delayed_work_sync(&hyp_clock->work);
-		hyp_clock->running = false;
+		return;
 	}
 
 	ktime_get_snapshot_id(CLOCK_BOOTTIME, &snap);
@@ -128,7 +123,6 @@ static void hyp_trace_clock_enable(struct hyp_trace_clock *hyp_clock, bool enabl
 	INIT_DELAYED_WORK(&hyp_clock->work, __hyp_clock_work);
 	schedule_delayed_work(&hyp_clock->work, msecs_to_jiffies(CLOCK_INIT_MS));
 	wait_for_completion(&hyp_clock->ready);
-	hyp_clock->running = true;
 }
 
 /* Access to this struct within the trace_remote_callbacks are protected by the trace_remote lock */
@@ -304,9 +298,15 @@ static void hyp_trace_unload(struct trace_buffer_desc *desc, void *priv)
 
 static int hyp_trace_enable_tracing(bool enable, void *priv)
 {
+	int ret;
+
 	hyp_trace_clock_enable(&hyp_clock, enable);
 
-	return kvm_call_hyp_nvhe(__tracing_enable, enable);
+	ret = kvm_call_hyp_nvhe(__tracing_enable, enable);
+	if (ret)
+		hyp_trace_clock_enable(&hyp_clock, !enable);
+
+	return ret;
 }
 
 static int hyp_trace_swap_reader_page(unsigned int cpu, void *priv)

base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
-- 
2.55.0.141.g00534a21ce-goog