Linux To Disable PCID For Intel Alder Lake & Raptor Lake Due To Issue With INVLPG

[phoronix]

Phoronix: Linux To Disable PCID For Intel Alder Lake & Raptor Lake Due To Issue With INVLPG

A patch is pending via x86/urgent to workaround an issue with Intel Alder Lake and Raptor Lake processors that is leaving the kernel developers for the time being to disable Process Context Identifiers (PCID) with these Intel mobile/desktop processors...

https://www.phoronix.com/news/Intel-Disable-PCID-ADL-RPL

[milkylainen]

Ok. So these modern CPUs must now resort to the old way of flushing the entire TLB at every context switch?
Sounds like an expensive fail.

[kobblestown]

Ok. So these modern CPUs must now resort to the old way of flushing the entire TLB at every context switch?
Sounds like an expensive fail.

Only if KPTI is used. But as the article notes, they are not affected by Meltdown so you can disable KPTI. And then most context switches will not invalidate TLBs.

I seem to remember KPTI even with PCID was a significant set back for performance. I don't know if Michael has performed such tests recently.

[jrtc27]

Intel's engineers are 5 months behind FreeBSD's developers: https://github.com/freebsd/freebsd-s...cb7fde9a45b94a.

[dkasak]

Addled Lake :P

[chrcoluk]

Intel's engineers are 5 months behind FreeBSD's developers: https://github.com/freebsd/freebsd-s...cb7fde9a45b94a.

Well looks FreeBSD as well as Linux there fix is to disable the feature, it prevents the brokenness but probably not satisfactory, Intel whatever they come up with will I suspect fix the issue whilst keeping PCID enabled.