Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 989 insertions, 0 deletions

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
new file mode 100644
index 000000000..88dc66ee1
--- /dev/null
+++ b/drivers/pci/p2pdma.c
@@ -0,0 +1,989 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI Peer 2 Peer DMA support.
+ *
+ * Copyright (c) 2016-2018, Logan Gunthorpe
+ * Copyright (c) 2016-2017, Microsemi Corporation
+ * Copyright (c) 2017, Christoph Hellwig
+ * Copyright (c) 2018, Eideticom Inc.
+ */
+
+#define pr_fmt(fmt) "pci-p2pdma: " fmt
+#include <linux/ctype.h>
+#include <linux/dma-map-ops.h>
+#include <linux/pci-p2pdma.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/genalloc.h>
+#include <linux/memremap.h>
+#include <linux/percpu-refcount.h>
+#include <linux/random.h>
+#include <linux/seq_buf.h>
+#include <linux/xarray.h>
+
+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)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	struct pci_p2pdma *p2pdma;
+	size_t size = 0;
+
+	rcu_read_lock();
+	p2pdma = rcu_dereference(pdev->p2pdma);
+	if (p2pdma && p2pdma->pool)
+		size = gen_pool_size(p2pdma->pool);
+	rcu_read_unlock();
+
+	return sysfs_emit(buf, "%zd\n", size);
+}
+static DEVICE_ATTR_RO(size);
+
+static ssize_t available_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	struct pci_p2pdma *p2pdma;
+	size_t avail = 0;
+
+	rcu_read_lock();
+	p2pdma = rcu_dereference(pdev->p2pdma);
+	if (p2pdma && p2pdma->pool)
+		avail = gen_pool_avail(p2pdma->pool);
+	rcu_read_unlock();
+
+	return sysfs_emit(buf, "%zd\n", avail);
+}
+static DEVICE_ATTR_RO(available);
+
+static ssize_t published_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	struct pci_p2pdma *p2pdma;
+	bool published = false;
+
+	rcu_read_lock();
+	p2pdma = rcu_dereference(pdev->p2pdma);
+	if (p2pdma)
+		published = p2pdma->p2pmem_published;
+	rcu_read_unlock();
+
+	return sysfs_emit(buf, "%d\n", published);
+}
+static DEVICE_ATTR_RO(published);
+
+static struct attribute *p2pmem_attrs[] = {
+	&dev_attr_size.attr,
+	&dev_attr_available.attr,
+	&dev_attr_published.attr,
+	NULL,
+};
+
+static const struct attribute_group p2pmem_group = {
+	.attrs = p2pmem_attrs,
+	.name = "p2pmem",
+};
+
+static void pci_p2pdma_release(void *data)
+{
+	struct pci_dev *pdev = data;
+	struct pci_p2pdma *p2pdma;
+
+	p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+	if (!p2pdma)
+		return;
+
+	/* Flush and disable pci_alloc_p2p_mem() */
+	pdev->p2pdma = NULL;
+	synchronize_rcu();
+
+	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)
+{
+	int error = -ENOMEM;
+	struct pci_p2pdma *p2p;
+
+	p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
+	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;
+
+	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
+	if (error)
+		goto out_pool_destroy;
+
+	error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
+	if (error)
+		goto out_pool_destroy;
+
+	rcu_assign_pointer(pdev->p2pdma, p2p);
+	return 0;
+
+out_pool_destroy:
+	gen_pool_destroy(p2p->pool);
+out:
+	devm_kfree(&pdev->dev, p2p);
+	return error;
+}
+
+/**
+ * pci_p2pdma_add_resource - add memory for use as p2p memory
+ * @pdev: the device to add the memory to
+ * @bar: PCI BAR to add
+ * @size: size of the memory to add, may be zero to use the whole BAR
+ * @offset: offset into the PCI BAR
+ *
+ * The memory will be given ZONE_DEVICE struct pages so that it may
+ * be used with any DMA request.
+ */
+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;
+	struct pci_p2pdma *p2pdma;
+	void *addr;
+	int error;
+
+	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
+		return -EINVAL;
+
+	if (offset >= pci_resource_len(pdev, bar))
+		return -EINVAL;
+
+	if (!size)
+		size = pci_resource_len(pdev, bar) - offset;
+
+	if (size + offset > pci_resource_len(pdev, bar))
+		return -EINVAL;
+
+	if (!pdev->p2pdma) {
+		error = pci_p2pdma_setup(pdev);
+		if (error)
+			return error;
+	}
+
+	p2p_pgmap = devm_kzalloc(&pdev->dev, sizeof(*p2p_pgmap), GFP_KERNEL);
+	if (!p2p_pgmap)
+		return -ENOMEM;
+
+	pgmap = &p2p_pgmap->pgmap;
+	pgmap->range.start = pci_resource_start(pdev, bar) + offset;
+	pgmap->range.end = pgmap->range.start + size - 1;
+	pgmap->nr_range = 1;
+	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
+
+	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);
+	if (IS_ERR(addr)) {
+		error = PTR_ERR(addr);
+		goto pgmap_free;
+	}
+
+	p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+	error = gen_pool_add_owner(p2pdma->pool, (unsigned long)addr,
+			pci_bus_address(pdev, bar) + offset,
+			range_len(&pgmap->range), dev_to_node(&pdev->dev),
+			&pgmap->ref);
+	if (error)
+		goto pages_free;
+
+	pci_info(pdev, "added peer-to-peer DMA memory %#llx-%#llx\n",
+		 pgmap->range.start, pgmap->range.end);
+
+	return 0;
+
+pages_free:
+	devm_memunmap_pages(&pdev->dev, pgmap);
+pgmap_free:
+	devm_kfree(&pdev->dev, pgmap);
+	return error;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_add_resource);
+
+/*
+ * Note this function returns the parent PCI device with a
+ * reference taken. It is the caller's responsibility to drop
+ * the reference.
+ */
+static struct pci_dev *find_parent_pci_dev(struct device *dev)
+{
+	struct device *parent;
+
+	dev = get_device(dev);
+
+	while (dev) {
+		if (dev_is_pci(dev))
+			return to_pci_dev(dev);
+
+		parent = get_device(dev->parent);
+		put_device(dev);
+		dev = parent;
+	}
+
+	return NULL;
+}
+
+/*
+ * Check if a PCI bridge has its ACS redirection bits set to redirect P2P
+ * TLPs upstream via ACS. Returns 1 if the packets will be redirected
+ * upstream, 0 otherwise.
+ */
+static int pci_bridge_has_acs_redir(struct pci_dev *pdev)
+{
+	int pos;
+	u16 ctrl;
+
+	pos = pdev->acs_cap;
+	if (!pos)
+		return 0;
+
+	pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);
+
+	if (ctrl & (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC))
+		return 1;
+
+	return 0;
+}
+
+static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
+{
+	if (!buf)
+		return;
+
+	seq_buf_printf(buf, "%s;", pci_name(pdev));
+}
+
+static bool cpu_supports_p2pdma(void)
+{
+#ifdef CONFIG_X86
+	struct cpuinfo_x86 *c = &cpu_data(0);
+
+	/* Any AMD CPU whose family ID is Zen or newer supports p2pdma */
+	if (c->x86_vendor == X86_VENDOR_AMD && c->x86 >= 0x17)
+		return true;
+#endif
+
+	return false;
+}
+
+static const struct pci_p2pdma_whitelist_entry {
+	unsigned short vendor;
+	unsigned short device;
+	enum {
+		REQ_SAME_HOST_BRIDGE	= 1 << 0,
+	} flags;
+} pci_p2pdma_whitelist[] = {
+	/* 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},
+	/* Intel SkyLake-E */
+	{PCI_VENDOR_ID_INTEL,	0x2030, 0},
+	{PCI_VENDOR_ID_INTEL,	0x2031, 0},
+	{PCI_VENDOR_ID_INTEL,	0x2032, 0},
+	{PCI_VENDOR_ID_INTEL,	0x2033, 0},
+	{PCI_VENDOR_ID_INTEL,	0x2020, 0},
+	{PCI_VENDOR_ID_INTEL,	0x09a2, 0},
+	{}
+};
+
+/*
+ * If the first device on host's root bus is either devfn 00.0 or a PCIe
+ * Root Port, return it.  Otherwise return NULL.
+ *
+ * We often use a devfn 00.0 "host bridge" in the pci_p2pdma_whitelist[]
+ * (though there is no PCI/PCIe requirement for such a device).  On some
+ * platforms, e.g., Intel Skylake, there is no such host bridge device, and
+ * pci_p2pdma_whitelist[] may contain a Root Port at any devfn.
+ *
+ * This function is similar to pci_get_slot(host->bus, 0), but it does
+ * not take the pci_bus_sem lock since __host_bridge_whitelist() must not
+ * sleep.
+ *
+ * For this to be safe, the caller should hold a reference to a device on the
+ * bridge, which should ensure the host_bridge device will not be freed
+ * or removed from the head of the devices list.
+ */
+static struct pci_dev *pci_host_bridge_dev(struct pci_host_bridge *host)
+{
+	struct pci_dev *root;
+
+	root = list_first_entry_or_null(&host->bus->devices,
+					struct pci_dev, bus_list);
+
+	if (!root)
+		return NULL;
+
+	if (root->devfn == PCI_DEVFN(0, 0))
+		return root;
+
+	if (pci_pcie_type(root) == PCI_EXP_TYPE_ROOT_PORT)
+		return root;
+
+	return NULL;
+}
+
+static bool __host_bridge_whitelist(struct pci_host_bridge *host,
+				    bool same_host_bridge, bool warn)
+{
+	struct pci_dev *root = pci_host_bridge_dev(host);
+	const struct pci_p2pdma_whitelist_entry *entry;
+	unsigned short vendor, device;
+
+	if (!root)
+		return false;
+
+	vendor = root->vendor;
+	device = root->device;
+
+	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;
+	}
+
+	if (warn)
+		pci_warn(root, "Host bridge not in P2PDMA whitelist: %04x:%04x\n",
+			 vendor, device);
+
+	return false;
+}
+
+/*
+ * 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 host_bridge_whitelist(struct pci_dev *a, struct pci_dev *b,
+				  bool warn)
+{
+	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, warn);
+
+	if (__host_bridge_whitelist(host_a, false, warn) &&
+	    __host_bridge_whitelist(host_b, false, warn))
+		return true;
+
+	return false;
+}
+
+static unsigned long map_types_idx(struct pci_dev *client)
+{
+	return (pci_domain_nr(client->bus) << 16) |
+		(client->bus->number << 8) | client->devfn;
+}
+
+/*
+ * Calculate the P2PDMA mapping type and distance between two PCI devices.
+ *
+ * If the two devices are the same PCI function, return
+ * PCI_P2PDMA_MAP_BUS_ADDR and a distance of 0.
+ *
+ * If they are two functions of the same device, return
+ * PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 (one hop up to the bridge,
+ * then one hop back down to another function of the same device).
+ *
+ * In the case where two devices are connected to the same PCIe switch,
+ * return a distance of 4. This corresponds to the following PCI tree:
+ *
+ *     -+  Root Port
+ *      \+ Switch Upstream Port
+ *       +-+ Switch Downstream Port 0
+ *       + \- Device A
+ *       \-+ Switch Downstream Port 1
+ *         \- Device B
+ *
+ * The distance is 4 because we traverse from Device A to Downstream Port 0
+ * to the common Switch Upstream Port, back down to Downstream Port 1 and
+ * then to Device B. The mapping type returned depends on the ACS
+ * redirection setting of the ports along the path.
+ *
+ * If ACS redirect is set on any port in the path, traffic between the
+ * devices will go through the host bridge, so return
+ * PCI_P2PDMA_MAP_THRU_HOST_BRIDGE; otherwise return
+ * PCI_P2PDMA_MAP_BUS_ADDR.
+ *
+ * Any two devices that have a data path that goes through the host bridge
+ * will consult a whitelist. If the host bridge is in the whitelist, return
+ * PCI_P2PDMA_MAP_THRU_HOST_BRIDGE with the distance set to the number of
+ * ports per above. If the device is not in the whitelist, return
+ * PCI_P2PDMA_MAP_NOT_SUPPORTED.
+ */
+static enum pci_p2pdma_map_type
+calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
+		int *dist, bool verbose)
+{
+	enum pci_p2pdma_map_type map_type = PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
+	struct pci_dev *a = provider, *b = client, *bb;
+	bool acs_redirects = false;
+	struct pci_p2pdma *p2pdma;
+	struct seq_buf acs_list;
+	int acs_cnt = 0;
+	int dist_a = 0;
+	int dist_b = 0;
+	char buf[128];
+
+	seq_buf_init(&acs_list, buf, sizeof(buf));
+
+	/*
+	 * Note, we don't need to take references to devices returned by
+	 * pci_upstream_bridge() seeing we hold a reference to a child
+	 * device which will already hold a reference to the upstream bridge.
+	 */
+	while (a) {
+		dist_b = 0;
+
+		if (pci_bridge_has_acs_redir(a)) {
+			seq_buf_print_bus_devfn(&acs_list, a);
+			acs_cnt++;
+		}
+
+		bb = b;
+
+		while (bb) {
+			if (a == bb)
+				goto check_b_path_acs;
+
+			bb = pci_upstream_bridge(bb);
+			dist_b++;
+		}
+
+		a = pci_upstream_bridge(a);
+		dist_a++;
+	}
+
+	*dist = dist_a + dist_b;
+	goto map_through_host_bridge;
+
+check_b_path_acs:
+	bb = b;
+
+	while (bb) {
+		if (a == bb)
+			break;
+
+		if (pci_bridge_has_acs_redir(bb)) {
+			seq_buf_print_bus_devfn(&acs_list, bb);
+			acs_cnt++;
+		}
+
+		bb = pci_upstream_bridge(bb);
+	}
+
+	*dist = dist_a + dist_b;
+
+	if (!acs_cnt) {
+		map_type = PCI_P2PDMA_MAP_BUS_ADDR;
+		goto done;
+	}
+
+	if (verbose) {
+		acs_list.buffer[acs_list.len-1] = 0; /* drop final semicolon */
+		pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
+			 pci_name(provider));
+		pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
+			 acs_list.buffer);
+	}
+	acs_redirects = true;
+
+map_through_host_bridge:
+	if (!cpu_supports_p2pdma() &&
+	    !host_bridge_whitelist(provider, client, acs_redirects)) {
+		if (verbose)
+			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));
+		map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
+	}
+done:
+	rcu_read_lock();
+	p2pdma = rcu_dereference(provider->p2pdma);
+	if (p2pdma)
+		xa_store(&p2pdma->map_types, map_types_idx(client),
+			 xa_mk_value(map_type), GFP_KERNEL);
+	rcu_read_unlock();
+	return map_type;
+}
+
+/**
+ * pci_p2pdma_distance_many - Determine the cumulative distance between
+ *	a p2pdma provider and the clients in use.
+ * @provider: p2pdma provider to check against the client list
+ * @clients: array of devices to check (NULL-terminated)
+ * @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, 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).
+ *
+ * "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)
+{
+	enum pci_p2pdma_map_type map;
+	bool not_supported = false;
+	struct pci_dev *pci_client;
+	int total_dist = 0;
+	int i, distance;
+
+	if (num_clients == 0)
+		return -1;
+
+	for (i = 0; i < num_clients; i++) {
+		pci_client = find_parent_pci_dev(clients[i]);
+		if (!pci_client) {
+			if (verbose)
+				dev_warn(clients[i],
+					 "cannot be used for peer-to-peer DMA as it is not a PCI device\n");
+			return -1;
+		}
+
+		map = calc_map_type_and_dist(provider, pci_client, &distance,
+					     verbose);
+
+		pci_dev_put(pci_client);
+
+		if (map == PCI_P2PDMA_MAP_NOT_SUPPORTED)
+			not_supported = true;
+
+		if (not_supported && !verbose)
+			break;
+
+		total_dist += distance;
+	}
+
+	if (not_supported)
+		return -1;
+
+	return total_dist;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);
+
+/**
+ * pci_has_p2pmem - check if a given PCI device has published any p2pmem
+ * @pdev: PCI device to check
+ */
+bool pci_has_p2pmem(struct pci_dev *pdev)
+{
+	struct pci_p2pdma *p2pdma;
+	bool res;
+
+	rcu_read_lock();
+	p2pdma = rcu_dereference(pdev->p2pdma);
+	res = p2pdma && p2pdma->p2pmem_published;
+	rcu_read_unlock();
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(pci_has_p2pmem);
+
+/**
+ * pci_p2pmem_find_many - find a peer-to-peer DMA memory device compatible with
+ *	the specified list of clients and shortest distance (as determined
+ *	by pci_p2pmem_dma())
+ * @clients: array of devices to check (NULL-terminated)
+ * @num_clients: number of client devices in the list
+ *
+ * If multiple devices are behind the same switch, the one "closest" to the
+ * client devices in use will be chosen first. (So if one of the providers is
+ * the same as one of the clients, that provider will be used ahead of any
+ * other providers that are unrelated). If multiple providers are an equal
+ * distance away, one will be chosen at random.
+ *
+ * Returns a pointer to the PCI device with a reference taken (use pci_dev_put
+ * to return the reference) or NULL if no compatible device is found. The
+ * found provider will also be assigned to the client list.
+ */
+struct pci_dev *pci_p2pmem_find_many(struct device **clients, int num_clients)
+{
+	struct pci_dev *pdev = NULL;
+	int distance;
+	int closest_distance = INT_MAX;
+	struct pci_dev **closest_pdevs;
+	int dev_cnt = 0;
+	const int max_devs = PAGE_SIZE / sizeof(*closest_pdevs);
+	int i;
+
+	closest_pdevs = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!closest_pdevs)
+		return NULL;
+
+	for_each_pci_dev(pdev) {
+		if (!pci_has_p2pmem(pdev))
+			continue;
+
+		distance = pci_p2pdma_distance_many(pdev, clients,
+						    num_clients, false);
+		if (distance < 0 || distance > closest_distance)
+			continue;
+
+		if (distance == closest_distance && dev_cnt >= max_devs)
+			continue;
+
+		if (distance < closest_distance) {
+			for (i = 0; i < dev_cnt; i++)
+				pci_dev_put(closest_pdevs[i]);
+
+			dev_cnt = 0;
+			closest_distance = distance;
+		}
+
+		closest_pdevs[dev_cnt++] = pci_dev_get(pdev);
+	}
+
+	if (dev_cnt)
+		pdev = pci_dev_get(closest_pdevs[prandom_u32_max(dev_cnt)]);
+
+	for (i = 0; i < dev_cnt; i++)
+		pci_dev_put(closest_pdevs[i]);
+
+	kfree(closest_pdevs);
+	return pdev;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_find_many);
+
+/**
+ * pci_alloc_p2pmem - allocate peer-to-peer DMA memory
+ * @pdev: the device to allocate memory from
+ * @size: number of bytes to allocate
+ *
+ * Returns the allocated memory or NULL on error.
+ */
+void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
+{
+	void *ret = NULL;
+	struct percpu_ref *ref;
+	struct pci_p2pdma *p2pdma;
+
+	/*
+	 * Pairs with synchronize_rcu() in pci_p2pdma_release() to
+	 * ensure pdev->p2pdma is non-NULL for the duration of the
+	 * read-lock.
+	 */
+	rcu_read_lock();
+	p2pdma = rcu_dereference(pdev->p2pdma);
+	if (unlikely(!p2pdma))
+		goto out;
+
+	ret = (void *)gen_pool_alloc_owner(p2pdma->pool, size, (void **) &ref);
+	if (!ret)
+		goto out;
+
+	if (unlikely(!percpu_ref_tryget_live_rcu(ref))) {
+		gen_pool_free(p2pdma->pool, (unsigned long) ret, size);
+		ret = NULL;
+		goto out;
+	}
+out:
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);
+
+/**
+ * pci_free_p2pmem - free peer-to-peer DMA memory
+ * @pdev: the device the memory was allocated from
+ * @addr: address of the memory that was allocated
+ * @size: number of bytes that were allocated
+ */
+void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
+{
+	struct percpu_ref *ref;
+	struct pci_p2pdma *p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+
+	gen_pool_free_owner(p2pdma->pool, (uintptr_t)addr, size,
+			(void **) &ref);
+	percpu_ref_put(ref);
+}
+EXPORT_SYMBOL_GPL(pci_free_p2pmem);
+
+/**
+ * pci_p2pmem_virt_to_bus - return the PCI bus address for a given virtual
+ *	address obtained with pci_alloc_p2pmem()
+ * @pdev: the device the memory was allocated from
+ * @addr: address of the memory that was allocated
+ */
+pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
+{
+	struct pci_p2pdma *p2pdma;
+
+	if (!addr)
+		return 0;
+
+	p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+	if (!p2pdma)
+		return 0;
+
+	/*
+	 * Note: when we added the memory to the pool we used the PCI
+	 * bus address as the physical address. So gen_pool_virt_to_phys()
+	 * actually returns the bus address despite the misleading name.
+	 */
+	return gen_pool_virt_to_phys(p2pdma->pool, (unsigned long)addr);
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_virt_to_bus);
+
+/**
+ * pci_p2pmem_alloc_sgl - allocate peer-to-peer DMA memory in a scatterlist
+ * @pdev: the device to allocate memory from
+ * @nents: the number of SG entries in the list
+ * @length: number of bytes to allocate
+ *
+ * Return: %NULL on error or &struct scatterlist pointer and @nents on success
+ */
+struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
+					 unsigned int *nents, u32 length)
+{
+	struct scatterlist *sg;
+	void *addr;
+
+	sg = kmalloc(sizeof(*sg), GFP_KERNEL);
+	if (!sg)
+		return NULL;
+
+	sg_init_table(sg, 1);
+
+	addr = pci_alloc_p2pmem(pdev, length);
+	if (!addr)
+		goto out_free_sg;
+
+	sg_set_buf(sg, addr, length);
+	*nents = 1;
+	return sg;
+
+out_free_sg:
+	kfree(sg);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_alloc_sgl);
+
+/**
+ * pci_p2pmem_free_sgl - free a scatterlist allocated by pci_p2pmem_alloc_sgl()
+ * @pdev: the device to allocate memory from
+ * @sgl: the allocated scatterlist
+ */
+void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl)
+{
+	struct scatterlist *sg;
+	int count;
+
+	for_each_sg(sgl, sg, INT_MAX, count) {
+		if (!sg)
+			break;
+
+		pci_free_p2pmem(pdev, sg_virt(sg), sg->length);
+	}
+	kfree(sgl);
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_free_sgl);
+
+/**
+ * pci_p2pmem_publish - publish the peer-to-peer DMA memory for use by
+ *	other devices with pci_p2pmem_find()
+ * @pdev: the device with peer-to-peer DMA memory to publish
+ * @publish: set to true to publish the memory, false to unpublish it
+ *
+ * Published memory can be used by other PCI device drivers for
+ * peer-2-peer DMA operations. Non-published memory is reserved for
+ * exclusive use of the device driver that registers the peer-to-peer
+ * memory.
+ */
+void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
+{
+	struct pci_p2pdma *p2pdma;
+
+	rcu_read_lock();
+	p2pdma = rcu_dereference(pdev->p2pdma);
+	if (p2pdma)
+		p2pdma->p2pmem_published = publish;
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
+
+static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
+						    struct device *dev)
+{
+	enum pci_p2pdma_map_type type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
+	struct pci_dev *provider = to_p2p_pgmap(pgmap)->provider;
+	struct pci_dev *client;
+	struct pci_p2pdma *p2pdma;
+	int dist;
+
+	if (!provider->p2pdma)
+		return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+
+	if (!dev_is_pci(dev))
+		return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+
+	client = to_pci_dev(dev);
+
+	rcu_read_lock();
+	p2pdma = rcu_dereference(provider->p2pdma);
+
+	if (p2pdma)
+		type = xa_to_value(xa_load(&p2pdma->map_types,
+					   map_types_idx(client)));
+	rcu_read_unlock();
+
+	if (type == PCI_P2PDMA_MAP_UNKNOWN)
+		return calc_map_type_and_dist(provider, client, &dist, true);
+
+	return type;
+}
+
+/**
+ * pci_p2pdma_map_segment - map an sg segment determining the mapping type
+ * @state: State structure that should be declared outside of the for_each_sg()
+ *	loop and initialized to zero.
+ * @dev: DMA device that's doing the mapping operation
+ * @sg: scatterlist segment to map
+ *
+ * This is a helper to be used by non-IOMMU dma_map_sg() implementations where
+ * the sg segment is the same for the page_link and the dma_address.
+ *
+ * Attempt to map a single segment in an SGL with the PCI bus address.
+ * The segment must point to a PCI P2PDMA page and thus must be
+ * wrapped in a is_pci_p2pdma_page(sg_page(sg)) check.
+ *
+ * Returns the type of mapping used and maps the page if the type is
+ * PCI_P2PDMA_MAP_BUS_ADDR.
+ */
+enum pci_p2pdma_map_type
+pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
+		       struct scatterlist *sg)
+{
+	if (state->pgmap != sg_page(sg)->pgmap) {
+		state->pgmap = sg_page(sg)->pgmap;
+		state->map = pci_p2pdma_map_type(state->pgmap, dev);
+		state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
+	}
+
+	if (state->map == PCI_P2PDMA_MAP_BUS_ADDR) {
+		sg->dma_address = sg_phys(sg) + state->bus_off;
+		sg_dma_len(sg) = sg->length;
+		sg_dma_mark_bus_address(sg);
+	}
+
+	return state->map;
+}
+
+/**
+ * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
+ *		to enable p2pdma
+ * @page: contents of the value to be stored
+ * @p2p_dev: returns the PCI device that was selected to be used
+ *		(if one was specified in the stored value)
+ * @use_p2pdma: returns whether to enable p2pdma or not
+ *
+ * Parses an attribute value to decide whether to enable p2pdma.
+ * The value can select a PCI device (using its full BDF device
+ * name) or a boolean (in any format kstrtobool() accepts). A false
+ * value disables p2pdma, a true value expects the caller
+ * to automatically find a compatible device and specifying a PCI device
+ * expects the caller to use the specific provider.
+ *
+ * pci_p2pdma_enable_show() should be used as the show operation for
+ * the attribute.
+ *
+ * Returns 0 on success
+ */
+int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
+			    bool *use_p2pdma)
+{
+	struct device *dev;
+
+	dev = bus_find_device_by_name(&pci_bus_type, NULL, page);
+	if (dev) {
+		*use_p2pdma = true;
+		*p2p_dev = to_pci_dev(dev);
+
+		if (!pci_has_p2pmem(*p2p_dev)) {
+			pci_err(*p2p_dev,
+				"PCI device has no peer-to-peer memory: %s\n",
+				page);
+			pci_dev_put(*p2p_dev);
+			return -ENODEV;
+		}
+
+		return 0;
+	} else if ((page[0] == '0' || page[0] == '1') && !iscntrl(page[1])) {
+		/*
+		 * If the user enters a PCI device that  doesn't exist
+		 * like "0000:01:00.1", we don't want kstrtobool to think
+		 * it's a '0' when it's clearly not what the user wanted.
+		 * So we require 0's and 1's to be exactly one character.
+		 */
+	} else if (!kstrtobool(page, use_p2pdma)) {
+		return 0;
+	}
+
+	pr_err("No such PCI device: %.*s\n", (int)strcspn(page, "\n"), page);
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_enable_store);
+
+/**
+ * pci_p2pdma_enable_show - show a configfs/sysfs attribute indicating
+ *		whether p2pdma is enabled
+ * @page: contents of the stored value
+ * @p2p_dev: the selected p2p device (NULL if no device is selected)
+ * @use_p2pdma: whether p2pdma has been enabled
+ *
+ * Attributes that use pci_p2pdma_enable_store() should use this function
+ * to show the value of the attribute.
+ *
+ * Returns 0 on success
+ */
+ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
+			       bool use_p2pdma)
+{
+	if (!use_p2pdma)
+		return sprintf(page, "0\n");
+
+	if (!p2p_dev)
+		return sprintf(page, "1\n");
+
+	return sprintf(page, "%s\n", pci_name(p2p_dev));
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);