linux-kernel - Re: [PATCH] x86: fix ref-counting bug in change_page

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Message-Id: <47668A82.76E4.0078.0@novell.com>
Date:	Mon, 17 Dec 2007 13:41:06 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	<tglx@...utronix.de>, "Andrew Morton" <akpm@...ux-foundation.org>,
	<mingo@...hat.com>, "Andi Kleen" <ak@...e.de>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86: fix ref-counting bug in change_page_attr()

>>> Ingo Molnar <mingo@...e.hu> 17.12.07 14:28 >>>
>
>* Jan Beulich <jbeulich@...ell.com> wrote:
>
>> When either calling change_page_attr() with the default attributes 
>> pages in the direct mapping have and a page's attributes already were 
>> set to the default or when changing the attributes from one 
>> non-default value to another, the reference counting broke, leading to 
>> either premature restoration of a large page or missing the 
>> opportunity to do so.
>> 
>> At the same time, make __PHYSICAL_MASK_SHIFT on 64-bits the value it 
>> architecturally ought to have.
>
>hm, does this patch fix any real bug seen live? (if yes then do you have 
>links to it, etc?) It would be a v2.6.24 fix in theory but it looks too 
>dangerous for that. So i've queued it up for v2.6.25, for the time 
>being.

I had run into the issue with experimental code of mine quite a while back
(i.e. I don't even recall what exactly I was doing back then). After that I
just continued to keep the fix (which I had submitted before, but which
collided with something in Andi's tree back then iirc).

Jan

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