linux-kernel - Re: [PATCH v3 08/10] x86/mtrr: let cache_aps_delayed_init replace mtrr_aps_delayed

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Message-ID: <c0872933-e046-0c5e-b63f-861d2d343794@suse.com>
Date:   Tue, 27 Sep 2022 12:14:42 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 08/10] x86/mtrr: let cache_aps_delayed_init replace
 mtrr_aps_delayed_init

On 27.09.22 12:10, Borislav Petkov wrote:
> On Tue, Sep 27, 2022 at 10:57:37AM +0200, Juergen Gross wrote:
>> TBH I don't see the point of having an accessor which is just setting a
>> variable to "true". But if you like it better, I can keep it.
> 
> Accessors are always better, no matter how silly. :)

Okay, then I'll keep it.

> But, in trying to grok your next patch - you really should split those
> more complex ones because they're a pain to review - I'm starting to
> wonder whether we could even remove mtrr_aps_delayed_init and make the
> delayed init the default.
> 
> Because, AFAICT, set_mtrr_aps_delayed_init() is called by default
> by native_smp_prepare_cpus(). Which is called by hyperv and
> arch/x86/xen/smp_hvm.c.
> 
> The only one that's not calling it is arch/x86/xen/smp_pv.c but that
> thing doesn't support MTRRs in the first place, right?

Correct.

> Which means, it doesn't need delayed MTRR init anyway.
> 
> Which would then mean that this would simplify this ugly logic even more.
> 
> Or am I missing an angle?

Yes: cpu hotplug.


Juergen

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