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SubjectRe: [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs
On Tue, Aug 09, 2022 at 08:49:47PM +0200, Borislav Petkov wrote:
> On Tue, Aug 09, 2022 at 11:38:03AM -0700, Ira Weiny wrote:
> > Thomas did a lot of work to make the entry code generic. So I was
> > keeping that work consistent. This also helps to ensure I did not miss
> > any places.
>
> How about you worry about the other arches when you actually cross that
> bridge?

I guess I miss understood the reasoning behind Thomas' work. No one mentioned
trying to isolate this to x86 during the PKS review.

>
> > I don't believe this is correct because instrumentation is not enabled
> > here.
>
> Why do you have to run
>
> arch_save_aux_pt_regs()
>
> with instrumentation enabled?

Sorry, that was carried over from the PKS series where I did need to call it.

I pulled this series over quickly to show basically what needed to be done.
But I did not review it for this detail.

>
> Patch 5 does
>
> + struct pt_regs_auxiliary *aux_pt_regs = &to_extended_pt_regs(regs)->aux;
> +
> + aux_pt_regs->cpu = raw_smp_processor_id();
>
> only?
>
> Why does that need to run with instrumentation enabled?

This does not.

Am I wrong that instrumentation begin/end are 0 overhead in production builds?

Ira

>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette

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