/dev/dax, pmem: direct access to persistent memory

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: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
new file mode 100644
index 000000000000..86ffbaa891ad
--- /dev/null
+++ b/drivers/dax/Kconfig
@@ -0,0 +1,25 @@
+menuconfig DEV_DAX
+        tristate "DAX: direct access to differentiated memory"
+        default m if NVDIMM_DAX
+        help
+          Support raw access to differentiated (persistence, bandwidth,
+          latency...) memory via an mmap(2) capable character
+          device.  Platform firmware or a device driver may identify a
+          platform memory resource that is differentiated from the
+          baseline memory pool.  Mappings of a /dev/daxX.Y device impose
+          restrictions that make the mapping behavior deterministic.
+
+if DEV_DAX
+
+config DEV_DAX_PMEM
+        tristate "PMEM DAX: direct access to persistent memory"
+        depends on NVDIMM_DAX
+        default DEV_DAX
+        help
+          Support raw access to persistent memory.  Note that this
+          driver consumes memory ranges allocated and exported by the
+          libnvdimm sub-system.
+
+          Say Y if unsure
+
+endif