service: vi: Retrieve vsync event once per display

The display vsync event can only be retrieved once per display. Returns VI::ResultPermissionDenied if we attempt to retrieve the vsync event for the same display.

Prevents games such as .hack//G.U. Last Recode from consuming all the handles in the handle table by spamming vsync event retrievals and allows it to go in game.

src/core/hle/service/vi/display/vi_display.cpp

@@ -19,6 +19,7 @@
 #include "core/hle/service/nvflinger/hos_binder_driver_server.h"
 #include "core/hle/service/vi/display/vi_display.h"
 #include "core/hle/service/vi/layer/vi_layer.h"
+#include "core/hle/service/vi/vi_results.h"
 
 namespace Service::VI {
 
@@ -55,8 +56,18 @@ const Layer& Display::GetLayer(std::size_t index) const {
     return *layers.at(index);
 }
 
-Kernel::KReadableEvent& Display::GetVSyncEvent() {
-    return vsync_event->GetReadableEvent();
+ResultVal<Kernel::KReadableEvent*> Display::GetVSyncEvent() {
+    if (got_vsync_event) {
+        return ResultPermissionDenied;
+    }
+
+    got_vsync_event = true;
+
+    return GetVSyncEventUnchecked();
+}
+
+Kernel::KReadableEvent* Display::GetVSyncEventUnchecked() {
+    return &vsync_event->GetReadableEvent();
 }
 
 void Display::SignalVSyncEvent() {

src/core/hle/service/vi/display/vi_display.h

@@ -9,6 +9,7 @@
 
 #include "common/common_funcs.h"
 #include "common/common_types.h"
+#include "core/hle/result.h"
 
 namespace Kernel {
 class KEvent;
@@ -73,8 +74,16 @@ public:
         return layers.size();
     }
 
-    /// Gets the readable vsync event.
-    Kernel::KReadableEvent& GetVSyncEvent();
+    /**
+     * Gets the internal vsync event.
+     *
+     * @returns The internal Vsync event if it has not yet been retrieved,
+     *          VI::ResultPermissionDenied otherwise.
+     */
+    [[nodiscard]] ResultVal<Kernel::KReadableEvent*> GetVSyncEvent();
+
+    /// Gets the internal vsync event.
+    Kernel::KReadableEvent* GetVSyncEventUnchecked();
 
     /// Signals the internal vsync event.
     void SignalVSyncEvent();
@@ -118,6 +127,7 @@ private:
 
     std::vector<std::unique_ptr<Layer>> layers;
     Kernel::KEvent* vsync_event{};
+    bool got_vsync_event{false};
 };
 
 } // namespace Service::VI