Re: [PATCH v10 04/15] x86/cpu: Set LASS CR4 bit as pinning sensitive

Sohil Mehta
2025-10-10T19:03:33Z

On 10/8/2025 9:52 AM, Edgecombe, Rick P wrote:
> And unlike the other bits that just got added easily, this
> one required infrastructure changes and extra patch. So wondered, hmm, is it
> worth it to do the extra patches?
>

Yeah, I reconsidered its usefulness as well.

Though, adding it to CR4 pinned mask is a net positive, even with the
extra patch. As part of the pinning enforcement, we get the warning if
LASS is turned off by accident. The bit gets reprogrammed automatically
which, even if not useful, wouldn't harm in any way.

Also, the changes to defer CR pinning enforcement seem to be useful
independent of LASS. Plus, the patch turned out to be simpler than I had
imagined.

> Yea, I agree it would be good to get a warning. The write may be triggered
> accidentally by a kernel bug. I agree with the patch, but just commenting my
> reasoning for the sake of discussion. Maybe we can tighten the reasoning in the
> log.
Will do.