// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright(c) 2017 Intel Corporation. All rights reserved.
 */
#include <linux/pagemap.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>
#include <linux/magic.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/uio.h>
#include <linux/dax.h>
#include <linux/fs.h>
#include <linux/cacheinfo.h>
#include "dax-private.h"

/**
 * struct dax_device - anchor object for dax services
 * @inode: core vfs
 * @cdev: optional character interface for "device dax"
 * @private: dax driver private data
 * @flags: state and boolean properties
 * @ops: operations for this device
 * @holder_data: holder of a dax_device: could be filesystem or mapped device
 * @holder_ops: operations for the inner holder
 */
struct dax_device {
        struct inode inode;
        struct cdev cdev;
        void *private;
        unsigned long flags;
        const struct dax_operations *ops;
        void *holder_data;
        const struct dax_holder_operations *holder_ops;
};

static dev_t dax_devt;
DEFINE_STATIC_SRCU(dax_srcu);
static struct vfsmount *dax_mnt;
static DEFINE_IDA(dax_minor_ida);
static struct kmem_cache *dax_cache __read_mostly;
static struct super_block *dax_superblock __read_mostly;

int dax_read_lock(void)
{
        return srcu_read_lock(&dax_srcu);
}
EXPORT_SYMBOL_GPL(dax_read_lock);

void dax_read_unlock(int id)
{
        srcu_read_unlock(&dax_srcu, id);
}
EXPORT_SYMBOL_GPL(dax_read_unlock);

#if defined(CONFIG_BLOCK) && defined(CONFIG_FS_DAX)
#include <linux/blkdev.h>

static DEFINE_XARRAY(dax_hosts);

int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk)
{
        return xa_insert(&dax_hosts, (unsigned long)disk, dax_dev, GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(dax_add_host);

void dax_remove_host(struct gendisk *disk)
{
        xa_erase(&dax_hosts, (unsigned long)disk);
}
EXPORT_SYMBOL_GPL(dax_remove_host);

/**
 * fs_dax_get_by_bdev() - temporary lookup mechanism for filesystem-dax
 * @bdev: block device to find a dax_device for
 * @start_off: returns the byte offset into the dax_device that @bdev starts
 * @holder: filesystem or mapped device inside the dax_device
 * @ops: operations for the inner holder
 */
struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev, u64 *start_off,
                void *holder, const struct dax_holder_operations *ops)
{
        struct dax_device *dax_dev;
        u64 part_size;
        int id;

        if (!blk_queue_dax(bdev->bd_disk->queue))
                return NULL;

        *start_off = get_start_sect(bdev) * SECTOR_SIZE;
        part_size = bdev_nr_sectors(bdev) * SECTOR_SIZE;
        if (*start_off % PAGE_SIZE || part_size % PAGE_SIZE) {
                pr_info("%pg: error: unaligned partition for dax\n", bdev);
                return NULL;
        }

        id = dax_read_lock();
        dax_dev = xa_load(&dax_hosts, (unsigned long)bdev->bd_disk);
        if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
                dax_dev = NULL;
        else if (holder) {
                if (!cmpxchg(&dax_dev->holder_data, NULL, holder))
                        dax_dev->holder_ops = ops;
                else
                        dax_dev = NULL;
        }
        dax_read_unlock(id);

        return dax_dev;
}
EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);

void fs_put_dax(struct dax_device *dax_dev, void *holder)
{
        if (dax_dev && holder &&
            cmpxchg(&dax_dev->holder_data, holder, NULL) == holder)
                dax_dev->holder_ops = NULL;
        put_dax(dax_dev);
}
EXPORT_SYMBOL_GPL(fs_put_dax);
#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */

enum dax_device_flags {
        /* !alive + rcu grace period == no new operations / mappings */
        DAXDEV_ALIVE,
        /* gate whether dax_flush() calls the low level flush routine */
        DAXDEV_WRITE_CACHE,
        /* flag to check if device supports synchronous flush */
        DAXDEV_SYNC,
        /* do not leave the caches dirty after writes */
        DAXDEV_NOCACHE,
        /* handle CPU fetch exceptions during reads */
        DAXDEV_NOMC,
};

/**
 * dax_direct_access() - translate a device pgoff to an absolute pfn
 * @dax_dev: a dax_device instance representing the logical memory range
 * @pgoff: offset in pages from the start of the device to translate
 * @nr_pages: number of consecutive pages caller can handle relative to @pfn
 * @mode: indicator on normal access or recovery write
 * @kaddr: output parameter that returns a virtual address mapping of pfn
 * @pfn: output parameter that returns an absolute pfn translation of @pgoff
 *
 * Return: negative errno if an error occurs, otherwise the number of
 * pages accessible at the device relative @pgoff.
 */
long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
                enum dax_access_mode mode, void **kaddr, unsigned long *pfn)
{
        long avail;

        if (!dax_dev)
                return -EOPNOTSUPP;

        if (!dax_alive(dax_dev))
                return -ENXIO;

        if (nr_pages < 0)
                return -EINVAL;

        avail = dax_dev->ops->direct_access(dax_dev, pgoff, nr_pages,
                        mode, kaddr, pfn);
        if (!avail)
                return -ERANGE;
        return min(avail, nr_pages);
}
EXPORT_SYMBOL_GPL(dax_direct_access);

size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
                size_t bytes, struct iov_iter *i)
{
        if (!dax_alive(dax_dev))
                return 0;

        /*
         * The userspace address for the memory copy has already been validated
         * via access_ok() in vfs_write, so use the 'no check' version to bypass
         * the HARDENED_USERCOPY overhead.
         */
        if (test_bit(DAXDEV_NOCACHE, &dax_dev->flags))
                return _copy_from_iter_flushcache(addr, bytes, i);
        return _copy_from_iter(addr, bytes, i);
}

size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
                size_t bytes, struct iov_iter *i)
{
        if (!dax_alive(dax_dev))
                return 0;

        /*
         * The userspace address for the memory copy has already been validated
         * via access_ok() in vfs_red, so use the 'no check' version to bypass
         * the HARDENED_USERCOPY overhead.
         */
        if (test_bit(DAXDEV_NOMC, &dax_dev->flags))
                return _copy_mc_to_iter(addr, bytes, i);
        return _copy_to_iter(addr, bytes, i);
}

int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
                        size_t nr_pages)
{
        int ret;

        if (!dax_alive(dax_dev))
                return -ENXIO;
        /*
         * There are no callers that want to zero more than one page as of now.
         * Once users are there, this check can be removed after the
         * device mapper code has been updated to split ranges across targets.
         */
        if (nr_pages != 1)
                return -EIO;

        ret = dax_dev->ops->zero_page_range(dax_dev, pgoff, nr_pages);
        return dax_mem2blk_err(ret);
}
EXPORT_SYMBOL_GPL(dax_zero_page_range);

size_t dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
                void *addr, size_t bytes, struct iov_iter *iter)
{
        if (!dax_dev->ops->recovery_write)
                return 0;
        return dax_dev->ops->recovery_write(dax_dev, pgoff, addr, bytes, iter);
}
EXPORT_SYMBOL_GPL(dax_recovery_write);

int dax_holder_notify_failure(struct dax_device *dax_dev, u64 off,
                              u64 len, int mf_flags)
{
        int rc, id;

        id = dax_read_lock();
        if (!dax_alive(dax_dev)) {
                rc = -ENXIO;
                goto out;
        }

        if (!dax_dev->holder_ops) {
                rc = -EOPNOTSUPP;
                goto out;
        }

        rc = dax_dev->holder_ops->notify_failure(dax_dev, off, len, mf_flags);
out:
        dax_read_unlock(id);
        return rc;
}
EXPORT_SYMBOL_GPL(dax_holder_notify_failure);

#ifdef CONFIG_ARCH_HAS_PMEM_API
void arch_wb_cache_pmem(void *addr, size_t size);
void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
{
        if (unlikely(!dax_write_cache_enabled(dax_dev)))
                return;

        arch_wb_cache_pmem(addr, size);
}
#else
void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
{
}
#endif
EXPORT_SYMBOL_GPL(dax_flush);

void dax_write_cache(struct dax_device *dax_dev, bool wc)
{
        if (wc)
                set_bit(DAXDEV_WRITE_CACHE, &dax_dev->flags);
        else
                clear_bit(DAXDEV_WRITE_CACHE, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(dax_write_cache);

bool dax_write_cache_enabled(struct dax_device *dax_dev)
{
        return test_bit(DAXDEV_WRITE_CACHE, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(dax_write_cache_enabled);

bool dax_synchronous(struct dax_device *dax_dev)
{
        return test_bit(DAXDEV_SYNC, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(dax_synchronous);

void set_dax_synchronous(struct dax_device *dax_dev)
{
        set_bit(DAXDEV_SYNC, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(set_dax_synchronous);

void set_dax_nocache(struct dax_device *dax_dev)
{
        set_bit(DAXDEV_NOCACHE, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(set_dax_nocache);

void set_dax_nomc(struct dax_device *dax_dev)
{
        set_bit(DAXDEV_NOMC, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(set_dax_nomc);

bool dax_alive(struct dax_device *dax_dev)
{
        lockdep_assert_held(&dax_srcu);
        return test_bit(DAXDEV_ALIVE, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(dax_alive);

/*
 * Note, rcu is not protecting the liveness of dax_dev, rcu is ensuring
 * that any fault handlers or operations that might have seen
 * dax_alive(), have completed.  Any operations that start after
 * synchronize_srcu() has run will abort upon seeing !dax_alive().
 *
 * Note, because alloc_dax() returns an ERR_PTR() on error, callers
 * typically store its result into a local variable in order to check
 * the result. Therefore, care must be taken to populate the struct
 * device dax_dev field make sure the dax_dev is not leaked.
 */
void kill_dax(struct dax_device *dax_dev)
{
        if (!dax_dev)
                return;

        if (dax_dev->holder_data != NULL)
                dax_holder_notify_failure(dax_dev, 0, U64_MAX,
                                MF_MEM_PRE_REMOVE);

        clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
        synchronize_srcu(&dax_srcu);

        /* clear holder data */
        dax_dev->holder_ops = NULL;
        dax_dev->holder_data = NULL;
}
EXPORT_SYMBOL_GPL(kill_dax);

void run_dax(struct dax_device *dax_dev)
{
        set_bit(DAXDEV_ALIVE, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(run_dax);

static struct inode *dax_alloc_inode(struct super_block *sb)
{
        struct dax_device *dax_dev;
        struct inode *inode;

        dax_dev = alloc_inode_sb(sb, dax_cache, GFP_KERNEL);
        if (!dax_dev)
                return NULL;

        inode = &dax_dev->inode;
        inode->i_rdev = 0;
        return inode;
}

static struct dax_device *to_dax_dev(struct inode *inode)
{
        return container_of(inode, struct dax_device, inode);
}

static void dax_free_inode(struct inode *inode)
{
        struct dax_device *dax_dev = to_dax_dev(inode);
        if (inode->i_rdev)
                ida_free(&dax_minor_ida, iminor(inode));
        kmem_cache_free(dax_cache, dax_dev);
}

static void dax_destroy_inode(struct inode *inode)
{
        struct dax_device *dax_dev = to_dax_dev(inode);
        WARN_ONCE(test_bit(DAXDEV_ALIVE, &dax_dev->flags),
                        "kill_dax() must be called before final iput()\n");
}

static const struct super_operations dax_sops = {
        .statfs = simple_statfs,
        .alloc_inode = dax_alloc_inode,
        .destroy_inode = dax_destroy_inode,
        .free_inode = dax_free_inode,
        .drop_inode = inode_just_drop,
};

static int dax_init_fs_context(struct fs_context *fc)
{
        struct pseudo_fs_context *ctx = init_pseudo(fc, DAXFS_MAGIC);
        if (!ctx)
                return -ENOMEM;
        ctx->ops = &dax_sops;
        return 0;
}

static struct file_system_type dax_fs_type = {
        .name           = "dax",
        .init_fs_context = dax_init_fs_context,
        .kill_sb        = kill_anon_super,
};

static int dax_test(struct inode *inode, void *data)
{
        dev_t devt = *(dev_t *) data;

        return inode->i_rdev == devt;
}

static int dax_set(struct inode *inode, void *data)
{
        dev_t devt = *(dev_t *) data;

        inode->i_rdev = devt;
        return 0;
}

static struct dax_device *dax_dev_get(dev_t devt)
{
        struct dax_device *dax_dev;
        struct inode *inode;

        inode = iget5_locked(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31),
                        dax_test, dax_set, &devt);

        if (!inode)
                return NULL;

        dax_dev = to_dax_dev(inode);
        if (inode_state_read_once(inode) & I_NEW) {
                set_bit(DAXDEV_ALIVE, &dax_dev->flags);
                inode->i_cdev = &dax_dev->cdev;
                inode->i_mode = S_IFCHR;
                inode->i_flags = S_DAX;
                mapping_set_gfp_mask(&inode->i_data, GFP_USER);
                unlock_new_inode(inode);
        }

        return dax_dev;
}

struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
{
        struct dax_device *dax_dev;
        dev_t devt;
        int minor;

        /*
         * Unavailable on architectures with virtually aliased data caches,
         * except for device-dax (NULL operations pointer), which does
         * not use aliased mappings from the kernel.
         */
        if (ops && cpu_dcache_is_aliasing())
                return ERR_PTR(-EOPNOTSUPP);

        if (WARN_ON_ONCE(ops && !ops->zero_page_range))
                return ERR_PTR(-EINVAL);

        minor = ida_alloc_max(&dax_minor_ida, MINORMASK, GFP_KERNEL);
        if (minor < 0)
                return ERR_PTR(-ENOMEM);

        devt = MKDEV(MAJOR(dax_devt), minor);
        dax_dev = dax_dev_get(devt);
        if (!dax_dev)
                goto err_dev;

        dax_dev->ops = ops;
        dax_dev->private = private;
        return dax_dev;

 err_dev:
        ida_free(&dax_minor_ida, minor);
        return ERR_PTR(-ENOMEM);
}
EXPORT_SYMBOL_GPL(alloc_dax);

void put_dax(struct dax_device *dax_dev)
{
        if (!dax_dev)
                return;
        iput(&dax_dev->inode);
}
EXPORT_SYMBOL_GPL(put_dax);

/**
 * dax_holder() - obtain the holder of a dax device
 * @dax_dev: a dax_device instance
 *
 * Return: the holder's data which represents the holder if registered,
 * otherwize NULL.
 */
void *dax_holder(struct dax_device *dax_dev)
{
        return dax_dev->holder_data;
}
EXPORT_SYMBOL_GPL(dax_holder);

/**
 * inode_dax: convert a public inode into its dax_dev
 * @inode: An inode with i_cdev pointing to a dax_dev
 *
 * Note this is not equivalent to to_dax_dev() which is for private
 * internal use where we know the inode filesystem type == dax_fs_type.
 */
struct dax_device *inode_dax(struct inode *inode)
{
        struct cdev *cdev = inode->i_cdev;

        return container_of(cdev, struct dax_device, cdev);
}
EXPORT_SYMBOL_GPL(inode_dax);

struct inode *dax_inode(struct dax_device *dax_dev)
{
        return &dax_dev->inode;
}
EXPORT_SYMBOL_GPL(dax_inode);

void *dax_get_private(struct dax_device *dax_dev)
{
        if (!test_bit(DAXDEV_ALIVE, &dax_dev->flags))
                return NULL;
        return dax_dev->private;
}
EXPORT_SYMBOL_GPL(dax_get_private);

static void init_once(void *_dax_dev)
{
        struct dax_device *dax_dev = _dax_dev;
        struct inode *inode = &dax_dev->inode;

        memset(dax_dev, 0, sizeof(*dax_dev));
        inode_init_once(inode);
}

static int dax_fs_init(void)
{
        int rc;

        dax_cache = kmem_cache_create("dax_cache", sizeof(struct dax_device), 0,
                        SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT | SLAB_ACCOUNT,
                        init_once);
        if (!dax_cache)
                return -ENOMEM;

        dax_mnt = kern_mount(&dax_fs_type);
        if (IS_ERR(dax_mnt)) {
                rc = PTR_ERR(dax_mnt);
                goto err_mount;
        }
        dax_superblock = dax_mnt->mnt_sb;

        return 0;

 err_mount:
        kmem_cache_destroy(dax_cache);

        return rc;
}

static void dax_fs_exit(void)
{
        kern_unmount(dax_mnt);
        rcu_barrier();
        kmem_cache_destroy(dax_cache);
}

static int __init dax_core_init(void)
{
        int rc;

        rc = dax_fs_init();
        if (rc)
                return rc;

        rc = alloc_chrdev_region(&dax_devt, 0, MINORMASK+1, "dax");
        if (rc)
                goto err_chrdev;

        rc = dax_bus_init();
        if (rc)
                goto err_bus;
        return 0;

err_bus:
        unregister_chrdev_region(dax_devt, MINORMASK+1);
err_chrdev:
        dax_fs_exit();
        return 0;
}

static void __exit dax_core_exit(void)
{
        dax_bus_exit();
        unregister_chrdev_region(dax_devt, MINORMASK+1);
        ida_destroy(&dax_minor_ida);
        dax_fs_exit();
}

MODULE_AUTHOR("Intel Corporation");
MODULE_DESCRIPTION("DAX: direct access to differentiated memory");
MODULE_LICENSE("GPL v2");
subsys_initcall(dax_core_init);
module_exit(dax_core_exit);