The device-dax implementation originally tried to be tricky and allow
private read-only mappings, but in the process allowed writable
MAP_PRIVATE + MAP_NORESERVE mappings.  For simplicity and predictability
just fail all private mapping attempts since device-dax memory is
statically allocated and will never support overcommit.

Cc: <stable@vger.kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Fixes: dee41079 ("/dev/dax, core: file operations and dax-mmap")
Reported-by: NPawel Lebioda <pawel.lebioda@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The dev_t variable in devm_create_dax_dev() is used before it's
first set:

drivers/dax/dax.c: In function 'devm_create_dax_dev':
drivers/dax/dax.c:205:39: error: 'dev_t' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  inode = iget5_locked(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31),
                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/dax/dax.c:688:8: note: 'dev_t' was declared here

This reorders the code to how it looks correct to me.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Fixes: 3bc52c45 ("dax: define a unified inode/address_space for device-dax mappings")
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

For sub-division support we need access to the dax_dev created by
devm_create_dax_dev().
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

pgoff_to_phys() validates that both the starting address and the length
of the mapping against the resource list.  We need to check for a
mapping size of PMD_SIZE not PAGE_SIZE in the pmd fault path.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

All the extents of a dax-device must match the alignment of the region.
Otherwise, we are unable to guarantee fault semantics of a given page
size.  The region must be self-consistent itself as well.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Invalidate all mappings of a device-dax instance when the device is
unregistered.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

In support of enabling resize / truncate of device-dax instances, define
a pseudo-fs to provide a unified inode/address space for vm operations.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

A goal of the device-DAX interface is to be able to support many
exclusive allocations (partitions) of performance / feature
differentiated memory.  This count may exceed the default minors limit
of 256.

As a result of switching to an embedded cdev the inode-to-dax_dev
conversion is simplified, as well as reference counting which can switch
to the cdev kobject lifetime.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The kref in dax_dev can be made redundant if the final put_device() on
the device associated with the dax_dev frees the dax_dev.  This can be
accomplished by embedding a struct device in struct dax_dev, open coding
device_create() and specifying a custom release method.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Shorten the prefix of the file operations to distinguish them from
operations on the struct device associated with the dax_dev.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

In order to convert devm_create_dax_dev() to use cdev, it will need
access to dax_fops. Move dax_fops and related function definitions
before devm_create_dax_dev().
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/dax/dax.c:75:6: warning: symbol 'dax_region_put' was not declared.
drivers/dax/dax.c:95:19: warning: symbol 'alloc_dax_region' was not declared.
drivers/dax/dax.c:173:5: warning: symbol 'devm_create_dax_dev' was not declared.
drivers/dax/pmem.c:27:17: warning: symbol 'to_dax_pmem' was not declared.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

If devm_add_action() fails, we are explicitly calling the cleanup to free
the resources allocated. Use the helper devm_add_action_or_reset()
and return directly in case of error, since the cleanup function
has been already called by the helper if there was any error.
Reported-by: NSudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: NVikas C Sajjan <vikas.cha.sajjan@hpe.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The "Device DAX" core enables dax mappings of performance / feature
differentiated memory.  An open mapping or file handle keeps the backing
struct device live, but new mappings are only possible while the device
is enabled.   Faults are handled under rcu_read_lock to synchronize
with the enabled state of the device.

Similar to the filesystem-dax case the backing memory may optionally
have struct page entries.  However, unlike fs-dax there is no support
for private mappings, or mappings that are not backed by media (see
use of zero-page in fs-dax).

Mappings are always guaranteed to match the alignment of the dax_region.
If the dax_region is configured to have a 2MB alignment, all mappings
are guaranteed to be backed by a pmd entry.  Contrast this determinism
with the fs-dax case where pmd mappings are opportunistic.  If userspace
attempts to force a misaligned mapping, the driver will fail the mmap
attempt.  See dax_dev_check_vma() for other scenarios that are rejected,
like MAP_PRIVATE mappings.

Cc: Hannes Reinecke <hare@suse.de>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: N"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Device DAX is the device-centric analogue of Filesystem DAX
(CONFIG_FS_DAX).  It allows memory ranges to be allocated and mapped
without need of an intervening file system.  Device DAX is strict,
precise and predictable.  Specifically this interface:

1/ Guarantees fault granularity with respect to a given page size (pte,
pmd, or pud) set at configuration time.

2/ Enforces deterministic behavior by being strict about what fault
scenarios are supported.

For example, by forcing MADV_DONTFORK semantics and omitting MAP_PRIVATE
support device-dax guarantees that a mapping always behaves/performs the
same once established.  It is the "what you see is what you get" access
mechanism to differentiated memory vs filesystem DAX which has
filesystem specific implementation semantics.

Persistent memory is the first target, but the mechanism is also
targeted for exclusive allocations of performance differentiated memory
ranges.

This commit is limited to the base device driver infrastructure to
associate a dax device with pmem range.

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>