RE: [PATCH v8 13/15] x86/split_lock: Enable split lock detection by default

From: Thomas Gleixner
Date: Thu Apr 25 2019 - 06:58:46 EST

On Thu, 25 Apr 2019, David Laight wrote:

> From: Fenghua Yu
> > Sent: 24 April 2019 20:33
> > A split locked access locks bus and degrades overall memory access
> > performance. When split lock detection feature is enumerated, enable
> > the feature by default by writing 1 to bit 29 in MSR TEST_CTL to find
> > any split lock issue.
> You can't enable this by default until ALL the known potentially
> misaligned locked memory operations have been fixed.

Errm? The result will be a WARN_ON() printed and no further damage. It's
not making anything worse than it is now. In fact we just should add a

WARN_ON_ONCE(!aligned_to_long(p)) to all the xxx_bit() operations.

so we catch them even when they do not trigger that #AC thingy.