In a PCIe environment, transactions aren't always required to
reach the root bus before being re-routed. Peer-to-peer DMA
may actually not be seen by the IOMMU in these cases. For
IOMMU groups, we want to provide IOMMU drivers a way to detect
these restrictions. Provided with a PCI device, pci_acs_enabled
returns the furthest downstream device with a complete PCI ACS
chain. This information can then be used in grouping to create
fully isolated groups. ACS chain logic extracted from libvirt.
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
drivers/pci/pci.c | 43 +++++++++++++++++++++++++++++++++++++++++++
include/linux/pci.h | 1 +
2 files changed, 44 insertions(+), 0 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 111569c..d7f05ce 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2358,6 +2358,49 @@ void pci_enable_acs(struct pci_dev *dev)
pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
}
+#define PCI_EXT_CAP_ACS_ENABLED (PCI_ACS_SV | PCI_ACS_RR | \
+ PCI_ACS_CR | PCI_ACS_UF)
+
+/**
+ * pci_acs_enabled - test ACS support in downstream chain
+ * @dev: starting PCI device
+ *
+ * Returns the furthest downstream device with an unbroken ACS chain. If
+ * ACS is enabled throughout the chain, the returned device is the same as
+ * the one passed in.
+ */
+struct pci_dev *pci_acs_enabled(struct pci_dev *dev)
+{
+ struct pci_dev *acs_dev;
+ int pos;
+ u16 ctrl;
+
+ if (!pci_is_root_bus(dev->bus))
+ acs_dev = pci_acs_enabled(dev->bus->self);
+ else
+ return dev;
+
+ /* If the chain is already broken, pass on the device */
+ if (acs_dev != dev->bus->self)
+ return acs_dev;
+
+ if (!pci_is_pcie(dev) || (dev->class >> 8) != PCI_CLASS_BRIDGE_PCI)
+ return dev;
+
+ if (dev->pcie_type != PCI_EXP_TYPE_DOWNSTREAM)
+ return dev;
+
+ pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
+ if (!pos)
+ return acs_dev;
+
+ pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
+ if ((ctrl & PCI_EXT_CAP_ACS_ENABLED) != PCI_EXT_CAP_ACS_ENABLED)
+ return acs_dev;
+
+ return dev;
+}
+
/**
* pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
* @dev: the PCI device
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 9910b5c..dc25da3 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1586,6 +1586,7 @@ static inline bool pci_is_pcie(struct pci_dev *dev)
}
void pci_request_acs(void);
+struct pci_dev *pci_acs_enabled(struct pci_dev *dev);
#define PCI_VPD_LRDT 0x80 /* Large Resource Data Type */
--
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