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Date: Thu, 19 Feb 2009 21:08:42 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
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To: Linus Torvalds <torvalds@linux-foundation.org>
cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       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: [git pull] changes for tip, and a nasty x86 page table bug 
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On Thu, 19 Feb 2009, Linus Torvalds wrote:

> 
> 
> On Thu, 19 Feb 2009, Steven Rostedt wrote:
> > 
> > In doing this change, I stumbled upon a nasty bug in the page handling
> > of the x86 code, where we can fall into a state where the PTE
> > has the RW bit set, but the PMD does not.
> 
> How do we ever have a PMD that is read-only? That sounds like a bug to 
> begin with. There's no reason to ever do that.

Patch 2/6 explains how this happened, and supplies the fix.

> 
> In fact, it should trigger the pmd_bad() tests if it ever happens, 
> wouldn't it? We want all the _KERNPG_TABLE bits to always be set, no?

I'm not sure what would do a pmd_bad check.

-- Steve