linux-kernel - Re: [PATCH v1 02/47] x86: mtrr: generalize run time disabling of MTRR

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Date:	Fri, 27 Mar 2015 14:40:17 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	luto@...capital.net, mingo@...hat.com, tglx@...utronix.de,
	hpa@...or.com, jgross@...e.com, JBeulich@...e.com, bp@...e.de,
	suresh.b.siddha@...el.com, venkatesh.pallipadi@...el.com,
	airlied@...hat.com, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, x86@...nel.org,
	xen-devel@...ts.xenproject.org,
	"Luis R. Rodriguez" <mcgrof@...e.com>, Ingo Molnar <mingo@...e.hu>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Antonino Daplas <adaplas@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	konrad.wilk@...cle.com, ville.syrjala@...ux.intel.com,
	david.vrabel@...rix.com, bhelgaas@...gle.com,
	Roger Pau Monné <roger.pau@...rix.com>,
	xen-devel@...ts.xensource.com
Subject: Re: [PATCH v1 02/47] x86: mtrr: generalize run time disabling of
 MTRR

On Fri, 2015-03-20 at 16:17 -0700, Luis R. Rodriguez wrote:
 :
> @@ -734,6 +742,7 @@ void __init mtrr_bp_init(void)
>  	}
>  
>  	if (mtrr_if) {
> +		mtrr_enabled = true;
>  		set_num_var_ranges();
>  		init_table();
>  		if (use_intel()) {
                        get_mtrr_state();

After setting mtrr_enabled to true, get_mtrr_state() reads
MSR_MTRRdefType and sets 'mtrr_state.enabled', which also indicates if
MTRRs are enabled or not on the system.  So, potentially, we could have
a case that mtrr_enabled is set to true, but mtrr_state.enabled is set
to disabled when MTRRs are disabled by BIOS.

Thanks,
-Toshi

ps.
I recently cleaned up this part of the MTRR code in the patch below,
which is currently available in the -mm & -next trees.
https://lkml.org/lkml/2015/3/24/1063




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