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Date:   Wed, 28 Sep 2022 18:12:24 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Juergen Gross <jgross@suse.com>
Cc:     xen-devel@lists.xenproject.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v3 08/10] x86/mtrr: let cache_aps_delayed_init replace
 mtrr_aps_delayed_init
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On Wed, Sep 28, 2022 at 03:43:56PM +0200, Juergen Gross wrote:
> Would you feel better with adding a new enum member CPUHP_AP_CACHECTRL_ONLINE?
> 
> This would avoid a possible source of failure during resume in case no slot
> for CPUHP_AP_ONLINE_DYN is found (quite improbable, but in theory possible).

Let's keep that in the bag for the time when we get to cross that bridge.

> You wouldn't want to do that there, as there are multiple places where
> pm_sleep_enable_secondary_cpus() is being called.

We want all of them, I'd say. They're all some sort of suspend AFAICT.
But yes, if we get to do it, that would need a proper audit.

> Additionally not all cases are coming in via
> pm_sleep_enable_secondary_cpus(), as there is e.g. a call of
> suspend_enable_secondary_cpus() from kernel_kexec(), which wants to
> have the same handling.

Which means, more hairy.

> arch_thaw_secondary_cpus_begin() and arch_thaw_secondary_cpus_end() are
> the functions to mark start and end of the special region where the
> delayed MTRR setup should happen.

Yap, it seems like the best solution at the moment. Want me to do a
proper patch and test it on real hw?

:-)

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette