From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758213Ab0JVSGZ (ORCPT ); Fri, 22 Oct 2010 14:06:25 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:33376 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753421Ab0JVSGX (ORCPT >); Fri, 22 Oct 2010 14:06:23 -0400 Date: Fri, 22 Oct 2010 14:05:51 -0400 From: Konrad Rzeszutek Wilk To: "H. Peter Anvin" Cc: Jeremy Fitzhardinge , 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 Message-ID: <20101022180551.GA26597@dumpdata.com> 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> <20101022180231.GA26365@dumpdata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101022180231.GA26365@dumpdata.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 22, 2010 at 02:02:31PM -0400, Konrad Rzeszutek Wilk wrote: > On Fri, Oct 22, 2010 at 09:44:08AM -0700, H. Peter Anvin wrote: > > On 10/22/2010 08:08 AM, Konrad Rzeszutek Wilk wrote: > > >> > > >> Okay, could you clarify this part a bit? Why does the kernel need to > > >> know the difference between "pseudo-physical" and "machine addresses" at > > >> all? If they overlap, there is a problem, and if they don't overlap, it > > >> will be a 1:1 mapping anyway... > > > > > > The flag (_PAGE_IOMAP) is used when we set the PTE so that the MFN value is > > > used instead of the PFN. We need that b/c when a driver does page_to_pfn() > > > it ends up using the PFN as bus address to write out registers data. > > > > > > Without this patch, the page->virt->PFN value is used and the PFN != to real MFN > > > so we end up writing in a memory address that the PCI device has no idea about. > > > By setting the PTE with the MFN, the virt->PFN gets the real MFN value. > > > > > > The drivers I am talking about are mostly, if not all, located in drivers/gpu > > > and it looks that we are missing two more patches to utilize the patch > > > that Jeremy posted. > > > > > > Please note that I am _not_ suggesting that the two patches > > > below should go out - I still need to post them on drm mailing list. > > > > > > > I'm still seriously confused. If I understand this correctly, we're > > talking about DMA addresses here (as opposed to PIO addresses, i.e. > > BARs), right? > > Correct. The BARs are ok since they go through the ioremap. Whoops. I answered that incorrectly. No, we are not talking about BARs. The BARs are ok (look at x86/PCI: make sure _PAGE_IOMAP it set on pci mappings patch, http://amailbox.org/mailarchive/linux-kernel/2010/10/12/4630930/thread) We are talking about the GPU's VM engine (or the GART on the Northbridge).