Re: [PATCH 1/2] x86: cpu/bugs: add support for AMD ERAPS feature

Andrew Cooper
2024-11-04T14:52:51Z

> Unfortunately, that's all we have right now in the official
> documentation.
>
> I've put up some notes in
> https://amitshah.net/2024/11/eraps-reduces-software-tax-for-hardware-bugs/

I appreciate the attempt to get a few details out, but this is very
confused on bunch of details.

Most importantly, you've described Intel RSB underflows, but named it
AMD BTC.

"Retbleed" is two totally different things.   I begged the discoverers
to give it two names, and I also begged the x86 maintainers to not alias
them in Linux's view of the world, but alas.

AMD's BTC comes from a bad branch type prediction, and a late resteer
from the ret uop executing.   It has nothing to do with RAS/RSB
underflow conditions.

~Andrew