linux-kernel - Re: [git pull] changes for tip, and a nasty x86 page table bug

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Message-ID: <alpine.DEB.1.10.0902192107230.31658@gandalf.stny.rr.com>
Date:	Thu, 19 Feb 2009 21:08:42 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [git pull] changes for tip, and a nasty x86 page table bug 


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

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