linux-kernel - Re: [PATCH v4 09/16] x86/mtrr: simplify mtrr_bp

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Message-ID: <Y1pQFjiVi9wajQH4@zn.tnic>
Date:   Thu, 27 Oct 2022 11:32:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.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 v4 09/16] x86/mtrr: simplify mtrr_bp_init()

On Tue, Oct 04, 2022 at 10:10:16AM +0200, Juergen Gross wrote:
> In case of the generic cache interface being used (Intel CPUs or a
> 64-bit system), the initialization sequence of the boot CPU is more
> complicated as necessary:

s/as/than/

> 
> - check if MTRR enabled, if yes, call mtrr_bp_pat_init() which will
>   disable caching, set the PAT MSR, and reenable caching
> 
> - call mtrr_cleanup(), in case that changed anything, call
>   cache_cpu_init() doing the same caching disable/enable dance as
>   above, but this time with setting the (modified) MTRR state (even
>   if MTRR was disabled) AND setting the PAT MSR (again even with
>   disabled MTRR)
> 
> The sequence can be simplified a lot while removing potential
> inconsistencies:
> 
> - check if MTRR enabled, if yes, call mtrr_cleanup() and then
>   cache_cpu_init()
> 
> This ensures to:
> 
> - no longer disable/enable caching more than once
> 
> - avoid to set MTRRs and/or the PAT MSR on the boot processor in case
>   of MTRR cleanups even if MTRRs meant to be disabled
> 
> With that mtrr_bp_pat_init() can be removed.

I like that simplification - I just hope there's not some weird ordering
that is still needed. But we'll see when this hits the wider audiences.

Thx.

-- 
Regards/Gruss,
    Boris.

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