Merge branch 'pci/p2pdma'

  - Move P2PCMA PCI bus offset from generic dev_pagemap to
    pci_p2pdma_pagemap (Logan Gunthorpe)

  - Add provider's pci_dev to pci_p2pdma_pagemap (Logan Gunthorpe)

  - Apply host bridge whitelist for ACS (Logan Gunthorpe)

  - Whitelist some Intel host bridges for P2PDMA (Logan Gunthorpe)

  - Add attrs to pci_p2pdma_map_sg() to match dma_map_sg() (Logan
    Gunthorpe)

  - Add pci_p2pdma_unmap_sg() (Logan Gunthorpe)

  - Store P2PDMA mapping method in xarray (Logan Gunthorpe)

  - Map requests that traverse a host bridge (Logan Gunthorpe)

  - Allow IOMMU for host bridge whitelist (Logan Gunthorpe)

* pci/p2pdma:
  PCI/P2PDMA: Update pci_p2pdma_distance_many() documentation
  PCI/P2PDMA: Allow IOMMU for host bridge whitelist
  PCI/P2PDMA: dma_map() requests that traverse the host bridge
  PCI/P2PDMA: Store mapping method in an xarray
  PCI/P2PDMA: Factor out __pci_p2pdma_map_sg()
  PCI/P2PDMA: Introduce pci_p2pdma_unmap_sg()
  PCI/P2PDMA: Add attrs argument to pci_p2pdma_map_sg()
  PCI/P2PDMA: Whitelist some Intel host bridges
  PCI/P2PDMA: Factor out host_bridge_whitelist()
  PCI/P2PDMA: Apply host bridge whitelist for ACS
  PCI/P2PDMA: Factor out __upstream_bridge_distance()
  PCI/P2PDMA: Add constants for map type results to upstream_bridge_distance()
  PCI/P2PDMA: Add provider's pci_dev to pci_p2pdma_pagemap struct
  PCI/P2PDMA: Introduce private pagemap structure

3 files changed, 276 insertions, 114 deletions

diff --git a/drivers/infiniband/core/rw.c b/drivers/infiniband/core/rw.c
index dce06108c8c3..5337393d4dfe 100644
--- a/drivers/infiniband/core/rw.c
+++ b/drivers/infiniband/core/rw.c
@@ -583,8 +583,10 @@ void rdma_rw_ctx_destroy(struct rdma_rw_ctx *ctx, struct ib_qp *qp, u8 port_num,
 		break;
 	}
 
-	/* P2PDMA contexts do not need to be unmapped */
-	if (!is_pci_p2pdma_page(sg_page(sg)))
+	if (is_pci_p2pdma_page(sg_page(sg)))
+		pci_p2pdma_unmap_sg(qp->pd->device->dma_device, sg,
+				    sg_cnt, dir);
+	else
 		ib_dma_unmap_sg(qp->pd->device, sg, sg_cnt, dir);
 }
 EXPORT_SYMBOL(rdma_rw_ctx_destroy);
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index bb970ca82517..2348b15f6bd0 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -547,8 +547,10 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
 
 	WARN_ON_ONCE(!iod->nents);
 
-	/* P2PDMA requests do not need to be unmapped */
-	if (!is_pci_p2pdma_page(sg_page(iod->sg)))
+	if (is_pci_p2pdma_page(sg_page(iod->sg)))
+		pci_p2pdma_unmap_sg(dev->dev, iod->sg, iod->nents,
+				    rq_dma_dir(req));
+	else
 		dma_unmap_sg(dev->dev, iod->sg, iod->nents, rq_dma_dir(req));
 
 
@@ -832,8 +834,8 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
 		goto out;
 
 	if (is_pci_p2pdma_page(sg_page(iod->sg)))
-		nr_mapped = pci_p2pdma_map_sg(dev->dev, iod->sg, iod->nents,
-					      rq_dma_dir(req));
+		nr_mapped = pci_p2pdma_map_sg_attrs(dev->dev, iod->sg,
+				iod->nents, rq_dma_dir(req), DMA_ATTR_NO_WARN);
 	else
 		nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents,
 					     rq_dma_dir(req), DMA_ATTR_NO_WARN);
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 234476226529..0608aae72ccc 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -18,13 +18,32 @@
 #include <linux/percpu-refcount.h>
 #include <linux/random.h>
 #include <linux/seq_buf.h>
-#include <linux/iommu.h>
+#include <linux/xarray.h>
+
+enum pci_p2pdma_map_type {
+	PCI_P2PDMA_MAP_UNKNOWN = 0,
+	PCI_P2PDMA_MAP_NOT_SUPPORTED,
+	PCI_P2PDMA_MAP_BUS_ADDR,
+	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
+};
 
 struct pci_p2pdma {
 	struct gen_pool *pool;
 	bool p2pmem_published;
+	struct xarray map_types;
 };
 
+struct pci_p2pdma_pagemap {
+	struct dev_pagemap pgmap;
+	struct pci_dev *provider;
+	u64 bus_offset;
+};
+
+static struct pci_p2pdma_pagemap *to_p2p_pgmap(struct dev_pagemap *pgmap)
+{
+	return container_of(pgmap, struct pci_p2pdma_pagemap, pgmap);
+}
+
 static ssize_t size_show(struct device *dev, struct device_attribute *attr,
 			 char *buf)
 {
@@ -87,6 +106,7 @@ static void pci_p2pdma_release(void *data)
 
 	gen_pool_destroy(p2pdma->pool);
 	sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
+	xa_destroy(&p2pdma->map_types);
 }
 
 static int pci_p2pdma_setup(struct pci_dev *pdev)
@@ -98,6 +118,8 @@ static int pci_p2pdma_setup(struct pci_dev *pdev)
 	if (!p2p)
 		return -ENOMEM;
 
+	xa_init(&p2p->map_types);
+
 	p2p->pool = gen_pool_create(PAGE_SHIFT, dev_to_node(&pdev->dev));
 	if (!p2p->pool)
 		goto out;
@@ -135,6 +157,7 @@ out:
 int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
 			    u64 offset)
 {
+	struct pci_p2pdma_pagemap *p2p_pgmap;
 	struct dev_pagemap *pgmap;
 	void *addr;
 	int error;
@@ -157,14 +180,18 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
 			return error;
 	}
 
-	pgmap = devm_kzalloc(&pdev->dev, sizeof(*pgmap), GFP_KERNEL);
-	if (!pgmap)
+	p2p_pgmap = devm_kzalloc(&pdev->dev, sizeof(*p2p_pgmap), GFP_KERNEL);
+	if (!p2p_pgmap)
 		return -ENOMEM;
+
+	pgmap = &p2p_pgmap->pgmap;
 	pgmap->res.start = pci_resource_start(pdev, bar) + offset;
 	pgmap->res.end = pgmap->res.start + size - 1;
 	pgmap->res.flags = pci_resource_flags(pdev, bar);
 	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
-	pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) -
+
+	p2p_pgmap->provider = pdev;
+	p2p_pgmap->bus_offset = pci_bus_address(pdev, bar) -
 		pci_resource_start(pdev, bar);
 
 	addr = devm_memremap_pages(&pdev->dev, pgmap);
@@ -246,19 +273,32 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
 	seq_buf_printf(buf, "%s;", pci_name(pdev));
 }
 
-/*
- * If we can't find a common upstream bridge take a look at the root
- * complex and compare it to a whitelist of known good hardware.
- */
-static bool root_complex_whitelist(struct pci_dev *dev)
+static const struct pci_p2pdma_whitelist_entry {
+	unsigned short vendor;
+	unsigned short device;
+	enum {
+		REQ_SAME_HOST_BRIDGE	= 1 << 0,
+	} flags;
+} pci_p2pdma_whitelist[] = {
+	/* AMD ZEN */
+	{PCI_VENDOR_ID_AMD,	0x1450,	0},
+
+	/* Intel Xeon E5/Core i7 */
+	{PCI_VENDOR_ID_INTEL,	0x3c00, REQ_SAME_HOST_BRIDGE},
+	{PCI_VENDOR_ID_INTEL,	0x3c01, REQ_SAME_HOST_BRIDGE},
+	/* Intel Xeon E7 v3/Xeon E5 v3/Core i7 */
+	{PCI_VENDOR_ID_INTEL,	0x2f00, REQ_SAME_HOST_BRIDGE},
+	{PCI_VENDOR_ID_INTEL,	0x2f01, REQ_SAME_HOST_BRIDGE},
+	{}
+};
+
+static bool __host_bridge_whitelist(struct pci_host_bridge *host,
+				    bool same_host_bridge)
 {
-	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
 	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
+	const struct pci_p2pdma_whitelist_entry *entry;
 	unsigned short vendor, device;
 
-	if (iommu_present(dev->dev.bus))
-		return false;
-
 	if (!root)
 		return false;
 
@@ -266,65 +306,49 @@ static bool root_complex_whitelist(struct pci_dev *dev)
 	device = root->device;
 	pci_dev_put(root);
 
-	/* AMD ZEN host bridges can do peer to peer */
-	if (vendor == PCI_VENDOR_ID_AMD && device == 0x1450)
+	for (entry = pci_p2pdma_whitelist; entry->vendor; entry++) {
+		if (vendor != entry->vendor || device != entry->device)
+			continue;
+		if (entry->flags & REQ_SAME_HOST_BRIDGE && !same_host_bridge)
+			return false;
+
 		return true;
+	}
 
 	return false;
 }
 
 /*
- * Find the distance through the nearest common upstream bridge between
- * two PCI devices.
- *
- * If the two devices are the same device then 0 will be returned.
- *
- * If there are two virtual functions of the same device behind the same
- * bridge port then 2 will be returned (one step down to the PCIe switch,
- * then one step back to the same device).
- *
- * In the case where two devices are connected to the same PCIe switch, the
- * value 4 will be returned. This corresponds to the following PCI tree:
- *
- *     -+  Root Port
- *      \+ Switch Upstream Port
- *       +-+ Switch Downstream Port
- *       + \- Device A
- *       \-+ Switch Downstream Port
- *         \- Device B
- *
- * The distance is 4 because we traverse from Device A through the downstream
- * port of the switch, to the common upstream port, back up to the second
- * downstream port and then to Device B.
- *
- * Any two devices that don't have a common upstream bridge will return -1.
- * In this way devices on separate PCIe root ports will be rejected, which
- * is what we want for peer-to-peer seeing each PCIe root port defines a
- * separate hierarchy domain and there's no way to determine whether the root
- * complex supports forwarding between them.
- *
- * In the case where two devices are connected to different PCIe switches,
- * this function will still return a positive distance as long as both
- * switches eventually have a common upstream bridge. Note this covers
- * the case of using multiple PCIe switches to achieve a desired level of
- * fan-out from a root port. The exact distance will be a function of the
- * number of switches between Device A and Device B.
- *
- * If a bridge which has any ACS redirection bits set is in the path
- * then this functions will return -2. This is so we reject any
- * cases where the TLPs are forwarded up into the root complex.
- * In this case, a list of all infringing bridge addresses will be
- * populated in acs_list (assuming it's non-null) for printk purposes.
+ * If we can't find a common upstream bridge take a look at the root
+ * complex and compare it to a whitelist of known good hardware.
  */
-static int upstream_bridge_distance(struct pci_dev *provider,
-				    struct pci_dev *client,
-				    struct seq_buf *acs_list)
+static bool host_bridge_whitelist(struct pci_dev *a, struct pci_dev *b)
+{
+	struct pci_host_bridge *host_a = pci_find_host_bridge(a->bus);
+	struct pci_host_bridge *host_b = pci_find_host_bridge(b->bus);
+
+	if (host_a == host_b)
+		return __host_bridge_whitelist(host_a, true);
+
+	if (__host_bridge_whitelist(host_a, false) &&
+	    __host_bridge_whitelist(host_b, false))
+		return true;
+
+	return false;
+}
+
+static enum pci_p2pdma_map_type
+__upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
+		int *dist, bool *acs_redirects, struct seq_buf *acs_list)
 {
 	struct pci_dev *a = provider, *b = client, *bb;
 	int dist_a = 0;
 	int dist_b = 0;
 	int acs_cnt = 0;
 
+	if (acs_redirects)
+		*acs_redirects = false;
+
 	/*
 	 * Note, we don't need to take references to devices returned by
 	 * pci_upstream_bridge() seeing we hold a reference to a child
@@ -353,15 +377,10 @@ static int upstream_bridge_distance(struct pci_dev *provider,
 		dist_a++;
 	}
 
-	/*
-	 * Allow the connection if both devices are on a whitelisted root
-	 * complex, but add an arbitrary large value to the distance.
-	 */
-	if (root_complex_whitelist(provider) &&
-	    root_complex_whitelist(client))
-		return 0x1000 + dist_a + dist_b;
+	if (dist)
+		*dist = dist_a + dist_b;
 
-	return -1;
+	return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
 
 check_b_path_acs:
 	bb = b;
@@ -378,33 +397,110 @@ check_b_path_acs:
 		bb = pci_upstream_bridge(bb);
 	}
 
-	if (acs_cnt)
-		return -2;
+	if (dist)
+		*dist = dist_a + dist_b;
+
+	if (acs_cnt) {
+		if (acs_redirects)
+			*acs_redirects = true;
+
+		return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
+	}
+
+	return PCI_P2PDMA_MAP_BUS_ADDR;
+}
+
+static unsigned long map_types_idx(struct pci_dev *client)
+{
+	return (pci_domain_nr(client->bus) << 16) |
+		(client->bus->number << 8) | client->devfn;
+}
+
+/*
+ * Find the distance through the nearest common upstream bridge between
+ * two PCI devices.
+ *
+ * If the two devices are the same device then 0 will be returned.
+ *
+ * If there are two virtual functions of the same device behind the same
+ * bridge port then 2 will be returned (one step down to the PCIe switch,
+ * then one step back to the same device).
+ *
+ * In the case where two devices are connected to the same PCIe switch, the
+ * value 4 will be returned. This corresponds to the following PCI tree:
+ *
+ *     -+  Root Port
+ *      \+ Switch Upstream Port
+ *       +-+ Switch Downstream Port
+ *       + \- Device A
+ *       \-+ Switch Downstream Port
+ *         \- Device B
+ *
+ * The distance is 4 because we traverse from Device A through the downstream
+ * port of the switch, to the common upstream port, back up to the second
+ * downstream port and then to Device B.
+ *
+ * Any two devices that cannot communicate using p2pdma will return
+ * PCI_P2PDMA_MAP_NOT_SUPPORTED.
+ *
+ * Any two devices that have a data path that goes through the host bridge
+ * will consult a whitelist. If the host bridges are on the whitelist,
+ * this function will return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE.
+ *
+ * If either bridge is not on the whitelist this function returns
+ * PCI_P2PDMA_MAP_NOT_SUPPORTED.
+ *
+ * If a bridge which has any ACS redirection bits set is in the path,
+ * acs_redirects will be set to true. In this case, a list of all infringing
+ * bridge addresses will be populated in acs_list (assuming it's non-null)
+ * for printk purposes.
+ */
+static enum pci_p2pdma_map_type
+upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
+		int *dist, bool *acs_redirects, struct seq_buf *acs_list)
+{
+	enum pci_p2pdma_map_type map_type;
+
+	map_type = __upstream_bridge_distance(provider, client, dist,
+					      acs_redirects, acs_list);
+
+	if (map_type == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE) {
+		if (!host_bridge_whitelist(provider, client))
+			map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
+	}
+
+	if (provider->p2pdma)
+		xa_store(&provider->p2pdma->map_types, map_types_idx(client),
+			 xa_mk_value(map_type), GFP_KERNEL);
 
-	return dist_a + dist_b;
+	return map_type;
 }
 
-static int upstream_bridge_distance_warn(struct pci_dev *provider,
-					 struct pci_dev *client)
+static enum pci_p2pdma_map_type
+upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
+			      int *dist)
 {
 	struct seq_buf acs_list;
+	bool acs_redirects;
 	int ret;
 
 	seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
 	if (!acs_list.buffer)
 		return -ENOMEM;
 
-	ret = upstream_bridge_distance(provider, client, &acs_list);
-	if (ret == -2) {
-		pci_warn(client, "cannot be used for peer-to-peer DMA as ACS redirect is set between the client and provider (%s)\n",
+	ret = upstream_bridge_distance(provider, client, dist, &acs_redirects,
+				       &acs_list);
+	if (acs_redirects) {
+		pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
 			 pci_name(provider));
 		/* Drop final semicolon */
 		acs_list.buffer[acs_list.len-1] = 0;
 		pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
 			 acs_list.buffer);
+	}
 
-	} else if (ret < 0) {
-		pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge\n",
+	if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED) {
+		pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge or whitelisted host bridge\n",
 			 pci_name(provider));
 	}
 
@@ -421,22 +517,22 @@ static int upstream_bridge_distance_warn(struct pci_dev *provider,
  * @num_clients: number of clients in the array
  * @verbose: if true, print warnings for devices when we return -1
  *
- * Returns -1 if any of the clients are not compatible (behind the same
- * root port as the provider), otherwise returns a positive number where
- * a lower number is the preferable choice. (If there's one client
- * that's the same as the provider it will return 0, which is best choice).
+ * Returns -1 if any of the clients are not compatible, otherwise returns a
+ * positive number where a lower number is the preferable choice. (If there's
+ * one client that's the same as the provider it will return 0, which is best
+ * choice).
  *
- * For now, "compatible" means the provider and the clients are all behind
- * the same PCI root port. This cuts out cases that may work but is safest
- * for the user. Future work can expand this to white-list root complexes that
- * can safely forward between each ports.
+ * "compatible" means the provider and the clients are either all behind
+ * the same PCI root port or the host bridges connected to each of the devices
+ * are listed in the 'pci_p2pdma_whitelist'.
  */
 int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
 			     int num_clients, bool verbose)
 {
 	bool not_supported = false;
 	struct pci_dev *pci_client;
-	int distance = 0;
+	int total_dist = 0;
+	int distance;
 	int i, ret;
 
 	if (num_clients == 0)
@@ -461,26 +557,26 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
 
 		if (verbose)
 			ret = upstream_bridge_distance_warn(provider,
-							    pci_client);
+					pci_client, &distance);
 		else
 			ret = upstream_bridge_distance(provider, pci_client,
-						       NULL);
+						       &distance, NULL, NULL);
 
 		pci_dev_put(pci_client);
 
-		if (ret < 0)
+		if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED)
 			not_supported = true;
 
 		if (not_supported && !verbose)
 			break;
 
-		distance += ret;
+		total_dist += distance;
 	}
 
 	if (not_supported)
 		return -1;
 
-	return distance;
+	return total_dist;
 }
 EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);
 
@@ -706,21 +802,19 @@ void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
 }
 EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
 
-/**
- * pci_p2pdma_map_sg - map a PCI peer-to-peer scatterlist for DMA
- * @dev: device doing the DMA request
- * @sg: scatter list to map
- * @nents: elements in the scatterlist
- * @dir: DMA direction
- *
- * Scatterlists mapped with this function should not be unmapped in any way.
- *
- * Returns the number of SG entries mapped or 0 on error.
- */
-int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
-		      enum dma_data_direction dir)
+static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider,
+						    struct pci_dev *client)
+{
+	if (!provider->p2pdma)
+		return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+
+	return xa_to_value(xa_load(&provider->p2pdma->map_types,
+				   map_types_idx(client)));
+}
+
+static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap,
+		struct device *dev, struct scatterlist *sg, int nents)
 {
-	struct dev_pagemap *pgmap;
 	struct scatterlist *s;
 	phys_addr_t paddr;
 	int i;
@@ -736,16 +830,80 @@ int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
 		return 0;
 
 	for_each_sg(sg, s, nents, i) {
-		pgmap = sg_page(s)->pgmap;
 		paddr = sg_phys(s);
 
-		s->dma_address = paddr - pgmap->pci_p2pdma_bus_offset;
+		s->dma_address = paddr - p2p_pgmap->bus_offset;
 		sg_dma_len(s) = s->length;
 	}
 
 	return nents;
 }
-EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);
+
+/**
+ * pci_p2pdma_map_sg - map a PCI peer-to-peer scatterlist for DMA
+ * @dev: device doing the DMA request
+ * @sg: scatter list to map
+ * @nents: elements in the scatterlist
+ * @dir: DMA direction
+ * @attrs: DMA attributes passed to dma_map_sg() (if called)
+ *
+ * Scatterlists mapped with this function should be unmapped using
+ * pci_p2pdma_unmap_sg_attrs().
+ *
+ * Returns the number of SG entries mapped or 0 on error.
+ */
+int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
+		int nents, enum dma_data_direction dir, unsigned long attrs)
+{
+	struct pci_p2pdma_pagemap *p2p_pgmap =
+		to_p2p_pgmap(sg_page(sg)->pgmap);
+	struct pci_dev *client;
+
+	if (WARN_ON_ONCE(!dev_is_pci(dev)))
+		return 0;
+
+	client = to_pci_dev(dev);
+
+	switch (pci_p2pdma_map_type(p2p_pgmap->provider, client)) {
+	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
+		return dma_map_sg_attrs(dev, sg, nents, dir, attrs);
+	case PCI_P2PDMA_MAP_BUS_ADDR:
+		return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents);
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg_attrs);
+
+/**
+ * pci_p2pdma_unmap_sg - unmap a PCI peer-to-peer scatterlist that was
+ *	mapped with pci_p2pdma_map_sg()
+ * @dev: device doing the DMA request
+ * @sg: scatter list to map
+ * @nents: number of elements returned by pci_p2pdma_map_sg()
+ * @dir: DMA direction
+ * @attrs: DMA attributes passed to dma_unmap_sg() (if called)
+ */
+void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
+		int nents, enum dma_data_direction dir, unsigned long attrs)
+{
+	struct pci_p2pdma_pagemap *p2p_pgmap =
+		to_p2p_pgmap(sg_page(sg)->pgmap);
+	enum pci_p2pdma_map_type map_type;
+	struct pci_dev *client;
+
+	if (WARN_ON_ONCE(!dev_is_pci(dev)))
+		return;
+
+	client = to_pci_dev(dev);
+
+	map_type = pci_p2pdma_map_type(p2p_pgmap->provider, client);
+
+	if (map_type == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE)
+		dma_unmap_sg_attrs(dev, sg, nents, dir, attrs);
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
 
 /**
  * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store