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

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Message-ID: <1415062233.10958.42.camel@misato.fc.hp.com>
Date:	Mon, 03 Nov 2014 17:50:33 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
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, 2014-11-03 at 23:53 +0100, Thomas Gleixner wrote:
> 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 for the background info about EXPORT_SYMBOL.  I will keep it no
change.

-Toshi

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