linux-kernel - Re: [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt

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Date:   Tue, 09 Aug 2022 23:14:19 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>, Ira Weiny <ira.weiny@...el.com>
Cc:     Rik van Riel <riel@...riel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary
 pt_regs

On Tue, Aug 09 2022 at 20:49, 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?

Ira is right. If we want it for everything, then the generic code is the
right place.

>> 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?
>
> 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?

There is no reason and actually _if_ we go there then this _has_ to
happen _before_ instrumentation comes into play as instrumentation might
want to have access to extended pt_regs. Not necessarily the cpu number,
but the other things which need to go there for a real reason.

Thanks,

        tglx