From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262286AbUBXPua (ORCPT ); Tue, 24 Feb 2004 10:50:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262289AbUBXPua (ORCPT ); Tue, 24 Feb 2004 10:50:30 -0500 Received: from amdext.amd.com ([139.95.251.1]:5538 "EHLO amdext.amd.com") by vger.kernel.org with ESMTP id S262286AbUBXPuU (ORCPT ); Tue, 24 Feb 2004 10:50:20 -0500 Message-ID: <99F2150714F93F448942F9A9F112634C0FD384E3@txexmtae.amd.com> From: richard.brunner@amd.com To: linux-kernel@vger.kernel.org Subject: RE: IOMMUs was Re: Intel vs AMD x86-64 Date: Tue, 24 Feb 2004 09:50:02 -0600 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2653.19) X-WSS-ID: 6C25AD134583306-01-01 Content-Type: text/plain Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Andi Kleen [mailto:ak@suse.de] > On Opteron the IOMMU code (ab)uses the built in AGPv3 GART in > the CPU, which > was originally intended for AGP. AMD converted it to be able > to remap PCI especially for Linux, which I think deserves applause. > > It works surprisingly well even though it was not designed as > a real IOMMU. Of course one of the main advantages of a real > IOMMU - preventing arbitary memory corruption from broken > devices - is lost because the remapping table is just a hole > in the memory. I'm > secretly hoping that when there is more support for Linux at > chipset vendors they will someday add a bit to isolate all > traffic that doesn't go through the GART from the main > memory. This way you could get a much more reliable system > that can tolerate broken PCI devices at a moderate > performance penalty. Andi is being modest. It was he and Andrea Arcangeli who convinced me we had a problem. We found a way to trick the AGP GART hardware into helping, and then they turned it into a "real" solution and helped us work the warts out of the BIOS to enable it.