X64 Clock: Reduce accuracy to be less or equal to guest accuracy.

2 files changed, 7 insertions, 1 deletions

diff --git a/src/common/x64/native_clock.cpp b/src/common/x64/native_clock.cpp
index 926f92ff8..f1bc60fd2 100644
--- a/src/common/x64/native_clock.cpp
+++ b/src/common/x64/native_clock.cpp
@@ -62,7 +62,8 @@ u64 NativeClock::GetRTSC() {
     }
     accumulated_ticks += diff;
     rtsc_serialize.unlock();
-    return accumulated_ticks;
+    /// The clock cannot be more precise than the guest timer, remove the lower bits
+    return accumulated_ticks & inaccuracy_mask;
 }
 
 void NativeClock::Pause(bool is_paused) {
diff --git a/src/common/x64/native_clock.h b/src/common/x64/native_clock.h
index 3851f8fc2..e853094d2 100644
--- a/src/common/x64/native_clock.h
+++ b/src/common/x64/native_clock.h
@@ -31,6 +31,11 @@ public:
 private:
     u64 GetRTSC();
 
+    /// value used to reduce the native clocks accuracy as some apss rely on
+    /// undefined behavior where the level of accuracy in the clock shouldn't
+    /// be higher.
+    static constexpr u64 inaccuracy_mask = ~(0x100 - 1);
+
     SpinLock rtsc_serialize{};
     u64 last_measure{};
     u64 accumulated_ticks{};