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

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Date:	Sat, 28 Mar 2015 00:56:30 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>, 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, 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, Mar 27, 2015 at 02:40:17PM -0600, Toshi Kani wrote:
> 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 for the review, in this case then we should update mtrr_enabled to false.

> 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

Great I will rebase and work with that and try to address this
consideration you have raised.

  Luis
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