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Date: Fri, 20 Feb 2009 09:02:46 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Huang Ying <ying.huang@intel.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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       Arjan van de Ven <arjan@infradead.org>,
       Rusty Russell <rusty@rustcorp.com.au>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH, v2] x86: use the right protections for split-up
	pagetables
Message-ID: <20090220080246.GA28669@elte.hu>
References: <20090220011316.379904625@goodmis.org> <alpine.LFD.2.00.0902191753240.21686@localhost.localdomain> <alpine.DEB.1.10.0902192107230.31658@gandalf.stny.rr.com> <alpine.LFD.2.00.0902191923300.21686@localhost.localdomain> <20090220072915.GB28085@elte.hu> <20090220073932.GA17648@elte.hu>
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* Ingo Molnar <mingo@elte.hu> wrote:

> [ Huang Ying also experienced problems in this area when writing
>   the EFI code, but the real bug in split_large_page() was not
>   realized back then. ]

> -	 * On Intel the NX bit of all levels must be cleared to make a
> -	 * page executable. See section 4.13.2 of Intel 64 and IA-32
> -	 * Architectures Software Developer's Manual).

Hm, in hindsight, we should have noticed this bug sooner - when 
the NX comment above was added. There's never any good reason to 
play protection games with higher-level pagetable entries. We 
dont do it to user-space pagetables either - we just populate 
them to _PAGE_TABLE and that's it.

	Ingo