This has nothing to do with variable length instructions. The issue here is that code the patch was designed to slow down… slowed down. Whodathunk? As for your

This has nothing to do with variable length instructions. The issue here is that code the patch was designed to slow down… slowed down. Whodathunk? As for your question, the LOCK prefix is only valid with a very select set of instructions. And those have to me of the mem/reg form (memory being read and written). If those conditions are not met, a hardware exception is raised.