Re: [PATCH] x86/alternatives: Disable KASAN on text_poke_early() in apply_alternatives()

Peter Zijlstra
2023-10-10T13:55:22Z

On Tue, Oct 10, 2023 at 03:10:54PM +0200, Borislav Petkov wrote:
> On Tue, Oct 10, 2023 at 12:10:56PM +0200, Peter Zijlstra wrote:
> > Now, obviously you really don't want boot_cpu_has() in
> > __VIRTUAL_MASK_SHIFT, that would be really bad (Linus recently
> > complained about how horrible the code-gen is around this already, must
> > not make it far worse).
>
> You mean a MOV (%rip) and a TEST are so horrible there because it is
> a mask?
>
> I'd experiment with it when I get a chance...

That gets you a memory-reference and potential cachemiss what should
have been an immediate :/