Re: [PATCH v16] x86/split_lock: Enable split lock detection by kernel

[Luck, Tony]

On Sat, Jan 25, 2020 at 04:34:29PM -0800, Andy Lutomirski wrote:
> Although I suppose the pile of wrmsrl_safes() in the existing patch
> might be sufficient.
> 
> All this being said, the current code appears wrong if a CPU is in the
> list but does have X86_FEATURE_CORE_CAPABILITIES.  Are there such
> CPUs?  I think either the logic should be changed or a comment should
> be added.

Is it really wrong? Code check the CPUID & CORE_CAPABILTIES first and
believes what they say. Otherwise falls back to the x86_match_cpu()
list.

I don't believe we put a CPU on that list that currently says
it supports CORE_CAPABILITIES. That could theoretically change
with a microcode update. I doubt we'd waste microcode space to do
that, but if we did, I assume we'd include the split lock bit
in the newly present MSR. So behavior would not change.

-Tony