linux-kernel - Re: [BUGFIX] x86_64: NX bit handling in change_page

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Date:	Wed, 12 Sep 2007 15:35:31 +0200
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Huang, Ying" <ying.huang@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX] x86_64: NX bit handling in change_page_attr


> > Index: linux-2.6.23-rc2-mm2/arch/x86_64/mm/pageattr.c
> > ===================================================================
> > --- linux-2.6.23-rc2-mm2.orig/arch/x86_64/mm/pageattr.c	2007-08-17
> > 12:50:25.000000000 +0800 +++
> > linux-2.6.23-rc2-mm2/arch/x86_64/mm/pageattr.c	2007-08-17
> > 12:50:48.000000000 +0800 @@ -147,6 +147,7 @@
> >  			split = split_large_page(address, prot, ref_prot2);
> >  			if (!split)
> >  				return -ENOMEM;
> > +			pgprot_val(ref_prot2) &= ~_PAGE_NX;
> >  			set_pte(kpte, mk_pte(split, ref_prot2));
> >  			kpte_page = split;
> >  		}
>
> What happened with this?  Still valid?

The bug is probably latent there, but I don't think it can affect anything
in the kernel because nothing in the kernel should change NX status
as far as I know.

Where did you see it? 

Anyways I would prefer to only clear the PMD NX when NX status actually 
changes on the PTE.Can you do that change? 

Anyways; it's really not very important.

-Andi
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