From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753371AbYIJR1w (ORCPT ); Wed, 10 Sep 2008 13:27:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751446AbYIJR1p (ORCPT ); Wed, 10 Sep 2008 13:27:45 -0400 Received: from gw.goop.org ([64.81.55.164]:43364 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751208AbYIJR1o (ORCPT ); Wed, 10 Sep 2008 13:27:44 -0400 Message-ID: <48C8038B.40107@goop.org> Date: Wed, 10 Sep 2008 10:27:39 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Nick Piggin CC: Avi Kivity , Ingo Molnar , Xen Devel , Andi Kleen , linux-kernel@vger.kernel.org, "H. Peter Anvin" Subject: Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag for IO mappings References: <4d93ba619c716c45cca0.1220826073@localhost> <48C7998D.1030408@qumranet.com> <48C7F80C.6000807@goop.org> <200809110255.03580.nickpiggin@yahoo.com.au> In-Reply-To: <200809110255.03580.nickpiggin@yahoo.com.au> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: > It complements vm_normal_page, which was there first (and coined by > Linus). It is the opposite of normal. This question always comes up > and my answer is always yes, if you can convince Linus to rename > vm_normal_page to the corresponding term :) > Not really. Normal is normal, but "special" doesn't tell us what kind of special it is. > It's not exactly _PAGE_NOSTRUCTPAGE. There can be struct pages under > there, but you're not to touch them. > To the extent that the struct page may as well not exist? Does it contain any meaningful state? Are they always IO mappings? Could we just use _PAGE_IOMAP as the name for _PAGE_SPECIAL? >>> And not having a struct page should correspond well to a pte not >>> requiring pfn->mfn conversion and being an I/O page. >>> >> But _PAGE_SPECIAL is only set in a few places. It's not set in ioremap >> mappings and so on. Should it be? >> > > Kernel address space, you mean? No, it is only ever used on user > addresses. > Right. But if we fold _PAGE_SPECIAL and _PAGE_IOMAP together, it would start getting used on kernel addresses (and obviously we'd need to rearrange _PAGE_CPA_TEST). >> There's also the hiccup that it gets set in a pte with pte_mkspecial() - >> but at that point its too late because you've already constructed the >> pte and done the pfn->mfn conversion. _PAGE_IOMAP can only be set when >> you initially construct the pte out of a frame number and a pgprot. >> > > I don't see this would be any problem because the pte is always constructed > in a single line in both places where it is used. > OK. If we were to fold these two together, then pte_mkspecial() would have to go, since it wouldn't possible to use correctly in my use case. J