Re: [RFC PATCH 00/16] x86/split_lock: Enable #AC exception for split locked accesses

[Peter Zijlstra]

On Sun, May 27, 2018 at 08:45:49AM -0700, Fenghua Yu wrote:
> Currently we can trace split lock event counter for debug purpose. But

How? A while ago I actually tried that, but I could not find a suitable
perf event.

> Intel introduces mechanism to detect split lock via alignment
> check exception in Tremont and other future processors. If split lock is
> from user process, #AC handler can kill the process or re-execute faulting
> instruction depending on configuration. 

Ideally it would #AC any unaligned (implied) LOCK prefix instruction,
not just across lines.

> To detect split lock, a new control bit (bit 29) in per-core TEST_CTL
> MSR 0x33 will be introduced in future x86 processors. When the bit 29
> is set, the processor causes #AC exception for split locked accesses at
> all CPL.

Per-Core is really unfortunate, but better than nothing.