Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel

[Luck, Tony]

On Sat, Jan 25, 2020 at 09:33:12PM +0100, Borislav Petkov wrote:
> On Sat, Jan 25, 2020 at 09:12:21PM +0100, Peter Zijlstra wrote:
> > My thinking was Virt, virt likes to mess up all msr expectations.
> 
> My only worry is to have it written down why we're doing this so that it
> can be changed/removed later, when we've forgotten all about split lock.
> Because pretty often we look at a comment-less chunk of code and wonder,
> "why the hell did we add this in the first place."

Ok. I added a comment:

 * Use the "safe" versions of rdmsr/wrmsr here because although code
 * checks CPUID and MSR bits to make sure the TEST_CTRL MSR should
 * exist, there may be glitches in virtualization that leave a guest
 * with an incorrect view of real h/w capabilities.

-Tony