ANDROID: KVM: arm64: Fix reset for hyp tracefs

While resetting the hypervisor tracing, the head page pointer wasn't
updated as well at the stamp and lost events. This might leave the
buffer in a corrupted state.

While at it, strengthen the reset test to check for timestamp and lost
events.

Bug: 357781595
Fixes: a368d579d1 ("FROMLIST: KVM: arm64: Add trace interface for hyp tracefs")
Change-Id: Ia5dac9634bcb3a2afea9db72ac6b2eda1d9a9730
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

arch/arm64/kvm/hyp/nvhe/trace.c

@@ -339,6 +339,11 @@ static int rb_cpu_reset(struct hyp_rb_per_cpu *cpu_buffer)
 
 	prev_status = rb_cpu_disable_writing(cpu_buffer);
 
+	if (!rb_set_head_page(cpu_buffer))
+		return -ENODEV;
+
+	cpu_buffer->tail_page = cpu_buffer->head_page;
+
 	bpage = cpu_buffer->head_page;
 	do {
 		rb_page_reset(bpage);
@@ -347,6 +352,9 @@ static int rb_cpu_reset(struct hyp_rb_per_cpu *cpu_buffer)
 
 	rb_page_reset(cpu_buffer->reader_page);
 
+	cpu_buffer->last_overrun = 0;
+	cpu_buffer->write_stamp = 0;
+
 	cpu_buffer->meta->reader.read = 0;
 	cpu_buffer->meta->reader.lost_events = 0;
 	cpu_buffer->meta->entries = 0;

tools/testing/selftests/hyp-trace/hyp-trace-test

@@ -208,8 +208,9 @@ test_reset()
     echo "Test Reset..."
 
     setup_hyp_trace
-    write_events 5
+    write_events 1000
     echo 0 > trace
+    clock_before=$(host_clock)
     write_events 5
 
     pid=$(consuming_read $tmp)
@@ -217,7 +218,7 @@ test_reset()
     stop_hyp_trace
     kill $pid
 
-    validate_test $tmp 5 0 $(host_clock)
+    validate_test $tmp 5 $clock_before $(host_clock)
 
     rm $tmp