[PATCH] Add memory barriers on some ASM functions
Certain instructions have memory side effects and having the compiler reorder
them is generally not a good thing. Eg modifying CR4_SMAP changes the way memory
fetches are done afterwards. Same with WRMSR on certain MSRs such as PAT, etc.
In practice I don't think there are conditions where they make a difference, but
for correctness, add memory barriers.