Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753826Ab3HVG4c (ORCPT ); Thu, 22 Aug 2013 02:56:32 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:55557 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753798Ab3HVG4b convert rfc822-to-8bit (ORCPT ); Thu, 22 Aug 2013 02:56:31 -0400 Message-Id: <5215D23A02000078000ED7FC@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.2 Date: Thu, 22 Aug 2013 07:56:26 +0100 From: "Jan Beulich" To: "Cyrill Gorcunov" Cc: "Andy Lutomirski" , "David Vrabel" , "Andrew Morton" , "Linus Torvalds" , , "Boris Ostrovsky" , "Konrad Rzeszutek Wilk" , "Pavel Emelyanov" , "Ingo Molnar" , "linux-kernel@vger.kernel.org" , "H. Peter Anvin" Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use References: <5214C524.1050900@citrix.com> <20130821141223.GS18673@moon> <5214F09002000078000ED5C3@nat28.tlf.novell.com> <20130821154238.GV18673@moon> <521500E102000078000ED65C@nat28.tlf.novell.com> <20130821161946.GW18673@moon> In-Reply-To: <20130821161946.GW18673@moon> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1402 Lines: 36 >>> On 21.08.13 at 18:19, Cyrill Gorcunov wrote: > On Wed, Aug 21, 2013 at 05:03:13PM +0100, Jan Beulich wrote: >> > >> > Only to non-present ptes, as far as I know. >> >> That's not really any guarantee. And the accessor functions also >> don't check that they'd be used on non-present PTEs only. > > Wait. This _PAGE_SWP_SOFT_DIRTY bit (which is in real PSE bit) assigned > in only one place -- in try_to_unmap_one(). The PTE get non-present then > and consists of swap entry format. I don't see any accessor to such entry > without testing if it's swap entry or pte-none. What I'm missing? Fact is that this static inline pte_t pte_swp_mksoft_dirty(pte_t pte) { return pte_set_flags(pte, _PAGE_SWP_SOFT_DIRTY); } has no checking whatsoever that the PTE being modified is a non-present one, not even in any of the debugging modes. It would be a different thing if the above acted on a swp_entry_t. The fact that there currently may be just a single call site (where the caller guarantees the non-present state) is no guarantee that in the future another one won't appear, and then result in very hard to debug problems. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/