From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758526Ab0JVTgq (ORCPT ); Fri, 22 Oct 2010 15:36:46 -0400 Received: from claw.goop.org ([74.207.240.146]:50099 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758271Ab0JVTgo (ORCPT ); Fri, 22 Oct 2010 15:36:44 -0400 Message-ID: <4CC1E7CB.8090106@goop.org> Date: Fri, 22 Oct 2010 12:36:43 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.4 MIME-Version: 1.0 To: "H. Peter Anvin" CC: Konrad Rzeszutek Wilk , the arch/x86 maintainers , "Xen-devel@lists.xensource.com" , Linux Kernel Mailing List Subject: Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP on VM_IO vmas References: <4CC0C14E.5080205@goop.org> <4CC0C318.90401@zytor.com> <4CC0CA07.3000306@goop.org> <4CC0DEB8.1060309@zytor.com> <20101022150826.GA23325@dumpdata.com> <4CC1BF58.9020001@zytor.com> <4CC1E0B6.3070303@goop.org> <4CC1E40F.60708@zytor.com> In-Reply-To: <4CC1E40F.60708@zytor.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/22/2010 12:20 PM, H. Peter Anvin wrote: > On 10/22/2010 12:06 PM, Jeremy Fitzhardinge wrote: >> Well, if you want to map a normal memory page, you'd use, say, >> pfn_pte(pfn, PAGE_KERNEL) to generate the pte. The pfn is a >> domain-local pseudo-physical address. When it ends up in >> xen_make_pte(), it will translate the the pfn into a machine-global mfn >> to generate a pte_t which can be inserted into a pagetable. (And when >> that pagetable starts being used as such, Xen will validate that the mfn >> is actually one the domain is allowed to address.) >> >> However, if you're doing an ioremap(), then the mapped address is a >> hardware one. In that case, we construct the pte with >> pfn_pte(device_pfn, PAGE_KERNEL_IO), which sets the _PAGE_IOMAP flag in >> the pte flags. When it gets to xen_make_pte(), it sees _PAGE_IOMAP and >> constructs a pte_t containing the literal untranslated device_pfn >> (really an mfn). (And again, Xen will check that the domain has access >> to that mfn before allowing the mapping to be used.) >> > When you're doing an ioremap(), then the mapped address is *both* a PFN > and an MFN, right? So why do your need a flag? That is the part I > don't get... Xen always needs an mfn, so for memory the pfn needs to be converted to an mfn, but for devices the frame number is already an mfn. You could look at it as having two distinct frame number address spaces, and the _PAGE_IOMAP flag tells the lower levels which address space the frame number is in. Both memory and device mappings use the same interface - __pte() - to convert a (pfn,prot) tuple into a pte_t, so we use a bit in prot to distinguish them. In the kernel, the places where device mappings vs memory mappings are quite well delineated. There used to be a few places which could be either depending on context, but they've since been cleaned up by other efforts (the PAT/pageattr work did a lot of them, I think). J