drivers/dax/super.c

// 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"
#include "bus.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);

#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */

#if IS_ENABLED(CONFIG_FS_DAX)

/**
 * fs_put_dax() - release holder ownership of a dax_device
 * @dax_dev: dax device to release (may be NULL)
 * @holder: the holder pointer previously passed to fs_dax_get() or
 *          fs_dax_get_by_bdev(); must match exactly, as it is used
 *          in a cmpxchg to atomically release ownership
 *
 * Must only be called by the current holder. Clears holder_ops before
 * holder_data to avoid a race where a concurrent fs_dax_get() could have
 * its newly installed holder_ops overwritten.
 */
void fs_put_dax(struct dax_device *dax_dev, void *holder)
{
	if (dax_dev && holder) {
		void *prev;

		/*
		 * Clear holder_ops before releasing holder_data. A concurrent
		 * dax_holder_notify_failure() that sees NULL ops returns
		 * -EOPNOTSUPP cleanly. A concurrent fs_dax_get() that acquires
		 * holder_data after the cmpxchg below is guaranteed to observe
		 * holder_ops=NULL first (cmpxchg provides release ordering), so
		 * its subsequent store of new ops will not be overwritten.
		 */
		WRITE_ONCE(dax_dev->holder_ops, NULL);
		prev = cmpxchg(&dax_dev->holder_data, holder, NULL);

		/*
		 * prev == holder: normal release.
		 * prev == NULL:   already released by kill_dax() when the
		 *                 device was removed under a live holder;
		 *                 not a bug.
		 * prev != holder (non-NULL): fs_put_dax() called by something
		 *                 that is not the current holder; an API
		 *                 contract violation. A lock would be needed
		 *                 to guard against this, but we WARN_ON()
		 *                 instead since violating the contract is
		 *                 a bug.
		 */
		WARN_ON(prev && prev != holder);
	}
	put_dax(dax_dev);
}
EXPORT_SYMBOL_GPL(fs_put_dax);

/**
 * fs_dax_get() - get ownership of a devdax via holder/holder_ops
 *
 * fs-dax file systems call this function to prepare to use a devdax device for
 * fsdax. This is like fs_dax_get_by_bdev(), but the caller already has struct
 * dev_dax (and there is no bdev). The holder makes this exclusive.
 *
 * @dax_dev: dev to be prepared for fs-dax usage
 * @holder: filesystem or mapped device inside the dax_device
 * @hops: operations for the inner holder
 *
 * Returns: 0 on success, <0 on failure
 */
int fs_dax_get(struct dax_device *dax_dev, void *holder,
	const struct dax_holder_operations *hops)
{
	struct dev_dax *dev_dax;
	struct dax_device_driver *dax_drv;
	int id;

	id = dax_read_lock();
	if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode)) {
		dax_read_unlock(id);
		return -ENODEV;
	}
	dax_read_unlock(id);

	/* Verify the device is bound to fsdev_dax driver */
	dev_dax = dax_get_private(dax_dev);
	if (!dev_dax) {
		iput(&dax_dev->inode);
		return -ENODEV;
	}

	device_lock(&dev_dax->dev);
	if (!dev_dax->dev.driver) {
		device_unlock(&dev_dax->dev);
		iput(&dax_dev->inode);
		return -ENODEV;
	}
	dax_drv = to_dax_drv(dev_dax->dev.driver);
	if (dax_drv->type != DAXDRV_FSDEV_TYPE) {
		device_unlock(&dev_dax->dev);
		iput(&dax_dev->inode);
		return -EOPNOTSUPP;
	}
	device_unlock(&dev_dax->dev);

	if (cmpxchg(&dax_dev->holder_data, NULL, holder)) {
		iput(&dax_dev->inode);
		return -EBUSY;
	}

	dax_dev->holder_ops = hops;

	return 0;
}
EXPORT_SYMBOL_GPL(fs_dax_get);
#endif /* 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 (!dax_dev->ops)
		return -EOPNOTSUPP;

	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;

	if (!dax_dev->ops)
		return -EOPNOTSUPP;

	/*
	 * 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 || !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)
{
	const struct dax_holder_operations *ops;
	int rc, id;

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

	/*
	 * Read holder_ops once: a concurrent fs_put_dax() can clear it without
	 * synchronizing against readers. Without the single fetch the compiler
	 * could reload between the NULL check and the call and dereference a
	 * NULL ops.
	 */
	ops = READ_ONCE(dax_dev->holder_ops);
	if (!ops) {
		rc = -EOPNOTSUPP;
		goto out;
	}

	rc = 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);

/**
 * dax_set_ops - set the dax_operations for a dax_device
 * @dax_dev: the dax_device to configure
 * @ops: the operations to set (may be NULL to clear)
 *
 * This allows drivers to set the dax_operations after the dax_device
 * has been allocated. This is needed when the device is created before
 * the driver that needs specific ops is bound (e.g., fsdev_dax binding
 * to a dev_dax created by hmem).
 *
 * When setting non-NULL ops, fails if ops are already set (returns -EBUSY).
 * When clearing ops (NULL), always succeeds.
 *
 * Return: 0 on success, -EBUSY if ops already set
 */
int dax_set_ops(struct dax_device *dax_dev, const struct dax_operations *ops)
{
	if (ops) {
		/* Setting ops: fail if already set */
		if (cmpxchg(&dax_dev->ops, NULL, ops) != NULL)
			return -EBUSY;
	} else {
		/* Clearing ops: always allowed */
		dax_dev->ops = NULL;
	}
	return 0;
}
EXPORT_SYMBOL_GPL(dax_set_ops);

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;
}

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;
}
EXPORT_SYMBOL_GPL(dax_dev_get);

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);