Re: [PATCH v7 02/26] x86/fpu/xstate: Refine CET user xstate bit enabling

[Peter Zijlstra]

On Tue, Nov 28, 2023 at 01:31:14AM +0000, Edgecombe, Rick P wrote:
> On Fri, 2023-11-24 at 10:40 +0100, Peter Zijlstra wrote:
> > So booting a host with "ibt=off" will clear the FEATURE_IBT, this was
> > fine before this patch-set, but possibly not with.
> > 
> > That kernel argument really only wants to tell the kernel not to use
> > IBT
> > itself, but not inhibit IBT from being used by guests.
> 
> Should we add a SW bit for it then? 

Don't think we need a feature flag for this, some boolean state should
be enough.

> ibt=off sounds like it should be
> turning off the whole feature though. It doesn't sound like kernel IBT
> specifically.

Well, the intent really was to just not enable IBT, clearing the feature
was the simplest way to make that happen.