Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755162Ab0LQPCe (ORCPT ); Fri, 17 Dec 2010 10:02:34 -0500 Received: from relay3.sgi.com ([192.48.152.1]:44656 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755134Ab0LQPCd (ORCPT ); Fri, 17 Dec 2010 10:02:33 -0500 To: linux-kernel@vger.kernel.org Subject: intel-iommu.c bug Cc: ashok.raj@intel.com, shaohua.li@intel.com, anil.s.keshavamurthy@intel.com, fenghua.yu@intel.com Message-Id: From: Cliff Wickman Date: Fri, 17 Dec 2010 09:03:19 -0600 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1698 Lines: 37 This bug was reported by Mike Habeck . The test system was an SGI Altix UV. These are Mike's words: It appears there is a bug in the iommu code that when 'forcedac' isn't used the nvidia driver is handed back a 44bit dma address even though it's dma_mask is set to 40bits. I added some debug to the intel_iommu code and I see: intel_map_sg(): dma_addr_t=0xf81fffff000, pdev->dma_mask=0xffffffffff Note the dma_addr_t being handed back is 44bits even though the mask is 40bits. This results in the nvidia card generating a bad dma (i.e. the nvidia hw is only capable of generating a 40bit dma address so the upper 4 bits are lost and that results in the iommu hw detecting a bad dma access): DRHD: handling fault status reg 2 DMAR:[DMA Read] Request device [36:00.0] fault addr 81fffff000 DMAR:[fault reason 06] PTE Read access is not set If I boot with 'forcedac' then the dma mask is honored and the dma_addr_t handed back is 40bits: intel_map_sg(): dma_addr_t=0xfffffff000, pdev->dma_mask=0xffffffffff Without forcedac you'd expect these early maps being handed back to be 32bits. This is the first debug printf (so the first mapping the nvidia device has requested) so I'd expect it to be 0xfffff000... interesting that is what the lower 32bits are in this address being handed back... that 0xf81 upper bits appear to be garbage bits. This might be a hint to help find the bug... -- 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/