From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752213Ab3HUOXt (ORCPT ); Wed, 21 Aug 2013 10:23:49 -0400 Received: from terminus.zytor.com ([198.137.202.10]:40126 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751485Ab3HUOXr (ORCPT ); Wed, 21 Aug 2013 10:23:47 -0400 User-Agent: K-9 Mail for Android In-Reply-To: <20130821141223.GS18673@moon> References: <5214C524.1050900@citrix.com> <20130821141223.GS18673@moon> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use From: "H. Peter Anvin" Date: Wed, 21 Aug 2013 16:22:44 +0200 To: Cyrill Gorcunov , David Vrabel CC: Andy Lutomirski , Pavel Emelyanov , Andrew Morton , Ingo Molnar , Xen-devel@lists.xen.org, "linux-kernel@vger.kernel.org" , Linus Torvalds , Konrad Rzeszutek Wilk , Boris Ostrovsky , Jan Beulich Message-ID: <035dc4d7-10e0-4e15-bdb4-3e353b271fe4@email.android.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Good question... Cyrill Gorcunov wrote: >On Wed, Aug 21, 2013 at 02:48:20PM +0100, David Vrabel wrote: >> All, >> >> 179ef71c (mm: save soft-dirty bits on swapped pages) introduces a new >> PTE bit on x86 _PTE_SWP_SOFT_DIRTY which has the same value as >_PTE_PSE >> and _PTE_PAT. >> >> With a Xen PV guest, the use of the _PTE_PAT will result in the page >> having unexpected cachability which will introduce a range of subtle >> performance and correctness issues. Xen programs the entry 4 in the >PAT >> table with WC so a page that was previously WB will end up as WC. >> > >David, could you please explain, Xen keeps and analyze _PTE_PAT bit >for ptes which are not present? -- Sent from my mobile phone. Please excuse brevity and lack of formatting.