[1/7] iommu: Create central IOMMU group lookup/creation interface

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index e5555fc..d061c86 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -29,6 +29,7 @@ 
 #include <linux/idr.h>
 #include <linux/notifier.h>
 #include <linux/err.h>
+#include <linux/pci.h>
 #include <trace/events/iommu.h>
 
 static struct kset *iommu_group_kset;
@@ -514,6 +515,187 @@  int iommu_group_id(struct iommu_group *group)
 }
 EXPORT_SYMBOL_GPL(iommu_group_id);
 
+/*
+ * To consider a PCI device isolated, we require ACS to support Source
+ * Validation, Request Redirection, Completer Redirection, and Upstream
+ * Forwarding.  This effectively means that devices cannot spoof their
+ * requester ID, requests and completions cannot be redirected, and all
+ * transactions are forwarded upstream, even as it passes through a
+ * bridge where the target device is downstream.
+ */
+#define REQ_ACS_FLAGS   (PCI_ACS_SV | PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF)
+
+struct group_for_pci_data {
+	struct pci_dev *pdev;
+	struct iommu_group *group;
+};
+
+/*
+ * DMA alias iterator callback, return the last seen device.  Stop and return
+ * the IOMMU group if we find one along the way.
+ */
+static int get_pci_alias_or_group(struct pci_dev *pdev, u16 alias, void *opaque)
+{
+	struct group_for_pci_data *data = opaque;
+
+	data->pdev = pdev;
+	data->group = iommu_group_get(&pdev->dev);
+
+	return data->group != NULL;
+}
+
+/*
+ * Use standard PCI bus topology, isolation features, and DMA alias quirks
+ * to find or create an IOMMU group for a device.
+ */
+static struct iommu_group *iommu_group_get_for_pci_dev(struct pci_dev *pdev)
+{
+	struct group_for_pci_data data;
+	struct pci_bus *bus;
+	struct iommu_group *group = NULL;
+	struct pci_dev *tmp;
+
+	/*
+	 * Find the upstream DMA alias for the device.  A device must not
+	 * be aliased due to topology in order to have its own IOMMU group.
+	 * If we find an alias along the way that already belongs to a
+	 * group, use it.
+	 */
+	if (pci_for_each_dma_alias(pdev, get_pci_alias_or_group, &data))
+		return data.group;
+
+	pdev = data.pdev;
+
+	/*
+	 * Continue upstream from the point of minimum IOMMU granularity
+	 * due to aliases to the point where devices are protected from
+	 * peer-to-peer DMA by PCI ACS.  Again, if we find an existing
+	 * group, use it.
+	 */
+	for (bus = pdev->bus; !pci_is_root_bus(bus); bus = bus->parent) {
+		if (!bus->self)
+			continue;
+
+		if (pci_acs_path_enabled(bus->self, NULL, REQ_ACS_FLAGS))
+			break;
+
+		pdev = bus->self;
+
+		group = iommu_group_get(&pdev->dev);
+		if (group)
+			return group;
+	}
+
+	/*
+	 * Next we need to consider DMA alias quirks.  If one device aliases
+	 * to another, they should be grouped together.  It's theoretically
+	 * possible that aliases could create chains of devices where each
+	 * device aliases another device.  If we then factor in multifunction
+	 * ACS grouping requirements, each alias could incorporate a new slot
+	 * with multiple functions, each with aliases.  This is all extremely
+	 * unlikely as DMA alias quirks are typically only used for PCIe
+	 * devices where we usually have a single slot per bus.  Furthermore,
+	 * the alias quirk is usually to another function within the slot
+	 * (and ACS multifunction is not supported) or to a different slot
+	 * that doesn't physically exist.  The likely scenario is therefore
+	 * that everything on the bus gets grouped together.  To reduce the
+	 * problem space, share the IOMMU group for all devices on the bus
+	 * if a DMA alias quirk is present on the bus.
+	 */
+	tmp = NULL;
+	for_each_pci_dev(tmp) {
+		if (tmp->bus != pdev->bus ||
+		    !(tmp->dev_flags & PCI_DEV_FLAGS_DMA_ALIAS_DEVFN))
+			continue;
+
+		pci_dev_put(tmp);
+		tmp = NULL;
+
+		/* We have an alias quirk, search for an existing group */
+		for_each_pci_dev(tmp) {
+			struct iommu_group *group_tmp;
+
+			if (tmp->bus != pdev->bus)
+				continue;
+
+			group_tmp = iommu_group_get(&tmp->dev);
+			if (!group) {
+				group = group_tmp;
+				continue;
+			}
+
+			if (group_tmp) {
+				WARN_ON(group != group_tmp);
+				iommu_group_put(group_tmp);
+			}
+		}
+
+		return group ? group : iommu_group_alloc();
+	}
+
+	/*
+	 * Non-multifunction devices or multifunction devices supporting
+	 * ACS get their own group.
+	 */
+	if (!pdev->multifunction || pci_acs_enabled(pdev, REQ_ACS_FLAGS))
+		return iommu_group_alloc();
+
+	/*
+	 * Multifunction devices not supporting ACS share a group with other
+	 * similar devices in the same slot.
+	 */
+	tmp = NULL;
+	for_each_pci_dev(tmp) {
+		if (tmp == pdev || tmp->bus != pdev->bus ||
+		    PCI_SLOT(tmp->devfn) !=  PCI_SLOT(pdev->devfn) ||
+		    pci_acs_enabled(tmp, REQ_ACS_FLAGS))
+			continue;
+
+		group = iommu_group_get(&tmp->dev);
+		if (group) {
+			pci_dev_put(tmp);
+			return group;
+		}
+	}
+
+	/* No shared group found, allocate new */
+	return iommu_group_alloc();
+}
+
+/**
+ * iommu_group_get_for_dev - Find or create the IOMMU group for a device
+ * @dev: target device
+ *
+ * This function is intended to be called by IOMMU drivers and extended to
+ * support common, bus-defined algorithms when determining or creating the
+ * IOMMU group for a device.  On success, the caller will hold a reference
+ * to the returned IOMMU group, which will already include the provided
+ * device.  The reference should be released with iommu_group_put().
+ */
+struct iommu_group *iommu_group_get_for_dev(struct device *dev)
+{
+	struct iommu_group *group = ERR_PTR(-EIO);
+	int ret;
+
+	group = iommu_group_get(dev);
+	if (group)
+		return group;
+
+	if (dev_is_pci(dev))
+		group = iommu_group_get_for_pci_dev(to_pci_dev(dev));
+
+	if (IS_ERR(group))
+		return group;
+
+	ret = iommu_group_add_device(group, dev);
+	if (ret) {
+		iommu_group_put(group);
+		return ERR_PTR(ret);
+	}
+
+	return group;
+}
+
 static int add_iommu_group(struct device *dev, void *data)
 {
 	struct iommu_ops *ops = data;
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index b96a5b2..a2e5843 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -181,6 +181,7 @@  extern int iommu_group_register_notifier(struct iommu_group *group,
 extern int iommu_group_unregister_notifier(struct iommu_group *group,
 					   struct notifier_block *nb);
 extern int iommu_group_id(struct iommu_group *group);
+extern struct iommu_group *iommu_group_get_for_dev(struct device *dev);
 
 extern int iommu_domain_get_attr(struct iommu_domain *domain, enum iommu_attr,
 				 void *data);