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

[Peter Zijlstra]

On Tue, May 29, 2018 at 09:40:09AM -0700, Dave Hansen wrote:
> Split-lock-detection is a new hardware feature that generates
> alignment-check (#AC) faults to help detect when badly-aligned atomic
> instructions might impact whole-system performance.  These patches are
> primarily targeted at application-level issues, but we can also detect
> the same issues in the kernel.

Which is nice, Thomas and me spend quite a while searching for a perf
event that could tell us about unaligned LOCK insns a few months back
and could not find anything useful.

> There is a significant interaction
> between this feature and firmware because firmware may or may not be
> prepared for this feature to be enabled.

And allowing firmware to muddle through, instead of drawing a hard line
in the sand means we'll be stuck with crap firmware for at least another
decade :/

Just say no.