Re: [PATCH v1 1/8] x86/entry/clearregs: Remove partial stack frame in fast system call

[Andi Kleen]

> What I mean is: this whole series is almost certainly a performance regression, it has no off switch, and is doesn't obviously solve any problem.  It' didn't qualify as a so.  And no one has benchmarked it. I think we should seriously consider just not applying it.

Well it's kernel hardening to guard against possible future speculation
attacks. Linus discussed it here for example:

https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1580667.html

For the on/off switch I can add a CONFIG to enable it, even though
it seems somewhat silly.

-Andi