From 3dfc813d94bba2046c6aed216e0fd69ac93a8e03 Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Sat, 4 Jul 2009 19:11:08 +0100 Subject: [PATCH] intel-iommu: Don't use identity mapping for PCI devices behind bridges Our current strategy for pass-through mode is to put all devices into the 1:1 domain at startup (which is before we know what their dma_mask will be), and only _later_ take them out of that domain, if it turns out that they really can't address all of memory. However, when there are a bunch of PCI devices behind a bridge, they all end up with the same source-id on their DMA transactions, and hence in the same IOMMU domain. This means that we _can't_ easily move them from the 1:1 domain into their own domain at runtime, because there might be DMA in-flight from their siblings. So we have to adjust our pass-through strategy: For PCI devices not on the root bus, and for the bridges which will take responsibility for their transactions, we have to start up _out_ of the 1:1 domain, just in case. This fixes the BUG() we see when we have 32-bit-capable devices behind a PCI-PCI bridge, and use the software identity mapping. It does mean that we might end up using 'normal' mapping mode for some devices which could actually live with the faster 1:1 mapping -- but this is only for PCI devices behind bridges, which presumably aren't the devices for which people are most concerned about performance. Signed-off-by: David Woodhouse --- drivers/pci/intel-iommu.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c index f9fc4f3..360fb67 100644 --- a/drivers/pci/intel-iommu.c +++ b/drivers/pci/intel-iommu.c @@ -2122,6 +2122,36 @@ static int iommu_should_identity_map(struct pci_dev *pdev, int startup) if (iommu_identity_mapping == 2) return IS_GFX_DEVICE(pdev); + /* + * We want to start off with all devices in the 1:1 domain, and + * take them out later if we find they can't access all of memory. + * + * However, we can't do this for PCI devices behind bridges, + * because all PCI devices behind the same bridge will end up + * with the same source-id on their transactions. + * + * Practically speaking, we can't change things around for these + * devices at run-time, because we can't be sure there'll be no + * DMA transactions in flight for any of their siblings. + * + * So PCI devices (unless they're on the root bus) as well as + * their parent PCI-PCI or PCIe-PCI bridges must be left _out_ of + * the 1:1 domain, just in _case_ one of their siblings turns out + * not to be able to map all of memory. + */ + if (!pdev->is_pcie) { + if (!pci_is_root_bus(pdev->bus)) + return 0; + if (pdev->class >> 8 == PCI_CLASS_BRIDGE_PCI) + return 0; + } else if (pdev->pcie_type == PCI_EXP_TYPE_PCI_BRIDGE) + return 0; + + /* + * At boot time, we don't yet know if devices will be 64-bit capable. + * Assume that they will -- if they turn out not to be, then we can + * take them out of the 1:1 domain later. + */ if (!startup) return pdev->dma_mask > DMA_BIT_MASK(32); -- 2.7.4