linux-kernel - Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use

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Message-ID: <4fec3e5b-695c-438b-ad6d-55ca50becc4c@email.android.com>
Date:	Wed, 21 Aug 2013 20:50:26 +0200
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>,
	David Vrabel <david.vrabel@...rix.com>
CC:	Jan Beulich <JBeulich@...e.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Xen-devel@...ts.xen.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use

But is there a manifest bug or not?  What is the deal with Xen?

Cyrill Gorcunov <gorcunov@...il.com> wrote:
>On Wed, Aug 21, 2013 at 09:25:47PM +0400, Cyrill Gorcunov wrote:
>> > 
>> > However, I do find the use of PTE bits in this way somewhat
>fragile.
>> > What other potential corner cases might still remain that will
>require
>> > further games with PTE bits?
>> 
>>   OK, so this is not a bug finally. The problem is that 2 level pte
>is
>> quite small and 7th bit is the only one spare I can use for soft
>dirty
>> tracking when page get swapped out. And swap engine is very depending
>> on pte being non-present, so we are on a safe side.
>
>To make it clear: I'm working on patch that won't use pse bit for dirty
>page tracking, just give some time to cook it and test.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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