Revert "unicode: Don't special case ignorable code points"

[linux.git] / drivers / pci / p2pdma.c

// 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 pci_dev *provider;
        u64 bus_offset;
        struct dev_pagemap pgmap;
};

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 int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
                const struct bin_attribute *attr, struct vm_area_struct *vma)
{
        struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
        size_t len = vma->vm_end - vma->vm_start;
        struct pci_p2pdma *p2pdma;
        struct percpu_ref *ref;
        unsigned long vaddr;
        void *kaddr;
        int ret;

        /* prevent private mappings from being established */
        if ((vma->vm_flags & VM_MAYSHARE) != VM_MAYSHARE) {
                pci_info_ratelimited(pdev,
                                     "%s: fail, attempted private mapping\n",
                                     current->comm);
                return -EINVAL;
        }

        if (vma->vm_pgoff) {
                pci_info_ratelimited(pdev,
                                     "%s: fail, attempted mapping with non-zero offset\n",
                                     current->comm);
                return -EINVAL;
        }

        rcu_read_lock();
        p2pdma = rcu_dereference(pdev->p2pdma);
        if (!p2pdma) {
                ret = -ENODEV;
                goto out;
        }

        kaddr = (void *)gen_pool_alloc_owner(p2pdma->pool, len, (void **)&ref);
        if (!kaddr) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * vm_insert_page() can sleep, so a reference is taken to mapping
         * such that rcu_read_unlock() can be done before inserting the
         * pages
         */
        if (unlikely(!percpu_ref_tryget_live_rcu(ref))) {
                ret = -ENODEV;
                goto out_free_mem;
        }
        rcu_read_unlock();

        for (vaddr = vma->vm_start; vaddr < vma->vm_end; vaddr += PAGE_SIZE) {
                ret = vm_insert_page(vma, vaddr, virt_to_page(kaddr));
                if (ret) {
                        gen_pool_free(p2pdma->pool, (uintptr_t)kaddr, len);
                        return ret;
                }
                percpu_ref_get(ref);
                put_page(virt_to_page(kaddr));
                kaddr += PAGE_SIZE;
                len -= PAGE_SIZE;
        }

        percpu_ref_put(ref);

        return 0;
out_free_mem:
        gen_pool_free(p2pdma->pool, (uintptr_t)kaddr, len);
out:
        rcu_read_unlock();
        return ret;
}

static struct bin_attribute p2pmem_alloc_attr = {
        .attr = { .name = "allocate", .mode = 0660 },
        .mmap = p2pmem_alloc_mmap,
        /*
         * Some places where we want to call mmap (ie. python) will check
         * that the file size is greater than the mmap size before allowing
         * the mmap to continue. To work around this, just set the size
         * to be very large.
         */
        .size = SZ_1T,
};

static struct attribute *p2pmem_attrs[] = {
        &dev_attr_size.attr,
        &dev_attr_available.attr,
        &dev_attr_published.attr,
        NULL,
};

static struct bin_attribute *p2pmem_bin_attrs[] = {
        &p2pmem_alloc_attr,
        NULL,
};

static const struct attribute_group p2pmem_group = {
        .attrs = p2pmem_attrs,
        .bin_attrs = p2pmem_bin_attrs,
        .name = "p2pmem",
};

static void p2pdma_page_free(struct page *page)
{
        struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(page->pgmap);
        /* safe to dereference while a reference is held to the percpu ref */
        struct pci_p2pdma *p2pdma =
                rcu_dereference_protected(pgmap->provider->p2pdma, 1);
        struct percpu_ref *ref;

        gen_pool_free_owner(p2pdma->pool, (uintptr_t)page_to_virt(page),
                            PAGE_SIZE, (void **)&ref);
        percpu_ref_put(ref);
}

static const struct dev_pagemap_ops p2pdma_pgmap_ops = {
        .page_free = p2pdma_page_free,
};

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;
}

static void pci_p2pdma_unmap_mappings(void *data)
{
        struct pci_dev *pdev = data;

        /*
         * Removing the alloc attribute from sysfs will call
         * unmap_mapping_range() on the inode, teardown any existing userspace
         * mappings and prevent new ones from being created.
         */
        sysfs_remove_file_from_group(&pdev->dev.kobj, &p2pmem_alloc_attr.attr,
                                     p2pmem_group.name);
}

/**
 * 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;
        pgmap->ops = &p2pdma_pgmap_ops;

        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;
        }

        error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_unmap_mappings,
                                         pdev);
        if (error)
                goto pages_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) | pci_dev_id(client);
}

/*
 * 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_ATOMIC);
        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
 * @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[get_random_u32_below(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;
        }
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);