Re: [PATCH v8 02/10] x86/bhi: Make clear_bhb_loop() effective on newer CPUs

David Laight
2026-03-26T10:46:01Z

On Thu, 26 Mar 2026 11:01:20 +0100
Borislav Petkov <bp@alien8.de> wrote:

> On Thu, Mar 26, 2026 at 01:39:34AM -0700, Pawan Gupta wrote:
> > I believe the equivalent for cpu_feature_enabled() in asm is the
> > ALTERNATIVE. Please let me know if I am missing something.
>
> Yes, you are.
>
> The point is that you don't want to stick those alternative calls inside some
> magic bhb_loop function but hand them in from the outside, as function
> arguments.
>
> Basically what I did.
>
> Then you were worried about this being C code and it had to be noinstr... So
> that outer function can be rewritten in asm, I think, and still keep it well
> separate.
>
> I'll try to rewrite it once I get a free minute, and see how it looks.
>

I think someone tried getting C code to write the values to global data
and getting the asm to read them.
That got discounted because it spilt things between two largely unrelated files.

I think the BPF code would need significant refactoring to call a C function.

David