Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()

[Linus Torvalds]

On Wed, 11 Oct 2023 at 00:45, Uros Bizjak <ubizjak@xxxxxxxxx> wrote:
>
> In fact, rdgsbase is available only for 64-bit targets.

Not even all 64-bit targets. That's why I did that ALTERNATIVE() thing
with X86_FEATURE_FSGSBASE, which uses the kernel instruction
re-writing.

So that suggested asm of mine defaults to loading the value from
memory through %gs, but with X86_FEATURE_FSGSBASE it gets rewritten to
use rdgsbase.

And again - I'm not sure it's any faster, but it's _potentially_
certainly better in that it doesn't use the cache-line.

           Linus