linux-kernel - Re: [PATCH v4 4/7] x86, mm, pat: Add pgprot

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Message-ID: <alpine.DEB.2.11.1411032352161.5308@nanos>
Date:	Mon, 3 Nov 2014 23:53:59 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Toshi Kani <toshi.kani@...com>
cc:	"Elliott, Robert (Server Storage)" <Elliott@...com>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jgross@...e.com" <jgross@...e.com>,
	"stefan.bader@...onical.com" <stefan.bader@...onical.com>,
	"luto@...capital.net" <luto@...capital.net>,
	"hmh@....eng.br" <hmh@....eng.br>,
	"yigal@...xistor.com" <yigal@...xistor.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>
Subject: Re: [PATCH v4 4/7] x86, mm, pat: Add pgprot_writethrough() for WT

On Mon, 3 Nov 2014, Toshi Kani wrote:
> On Mon, 2014-11-03 at 22:10 +0000, Elliott, Robert (Server Storage)
> wrote:
>  :
> > > Subject: [PATCH v4 4/7] x86, mm, pat: Add pgprot_writethrough() for
> > > WT
> > > 
> > > This patch adds pgprot_writethrough() for setting WT to a given
> > > pgprot_t.
> > > 
> > > Signed-off-by: Toshi Kani <toshi.kani@...com>
> > > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > ...
> > > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> > > index a214f5a..a0264d3 100644
> > > --- a/arch/x86/mm/pat.c
> > > +++ b/arch/x86/mm/pat.c
> > > @@ -896,6 +896,16 @@ pgprot_t pgprot_writecombine(pgprot_t prot)
> > >  }
> > >  EXPORT_SYMBOL_GPL(pgprot_writecombine);
> > > 
> > > +pgprot_t pgprot_writethrough(pgprot_t prot)
> > > +{
> > > +	if (pat_enabled)
> > > +		return __pgprot(pgprot_val(prot) |
> > > +				cachemode2protval(_PAGE_CACHE_MODE_WT));
> > > +	else
> > > +		return pgprot_noncached(prot);
> > > +}
> > > +EXPORT_SYMBOL_GPL(pgprot_writethrough);
> > ...
> > 
> > Would you be willing to use EXPORT_SYMBOL for the new 
> > pgprot_writethrough function to provide more flexibility
> > for modules to utilize the new feature?  In x86/mm, 18 of 60
> > current exports are GPL and 42 are not GPL.
> 
> I simply used EXPORT_SYMBOL_GPL() since pgprot_writecombine() used
> it. :-)  This interface is intended to be used along with
> remap_pfn_range() and ioremap_prot(), which are both exported with
> EXPORT_SYMBOL().  So, it seems reasonable to export it with
> EXPORT_SYMBOL() as well.  I will make this change.

NAK.

This is new functionality and we really have no reason to give the GPL
circumventors access to it.

Thanks,

	tglx
	
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