[PATCH 0/1] nvdimm: allow exposing RAM as libnvdimm DIMMs

[Mike Rapoport <rppt@kernel.org>]

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

Hi,

It's not uncommon that libnvdimm/dax/ndctl are used with normal volatile
memory for a whole bunch of $reasons.

Probably the most common usecase is to back VMs memory with fsdax/devdax,
but there are others as well when there's a requirement to manage memory
separately from the kernel.

The existing mechanisms to expose normal ram as "persistent", such as
memmap=x!y on x86 or dummy pmem-region device tree nodes on DT systems lack
flexibility to dynamically partition a single region without rebooting the
system and sometimes even updating the system firmware. Also, to create
several DAX devices with different properties it's necessary to repeat
the memmap= command line option or add several pmem-region nodes to the
DT.

I propose a new driver that will create a DIMM device on
E820_TYPE_PRAM/pmem-region and that will allow partitioning that device
dynamically. The label area is kept in the end of that region and managed
by the driver.

Changes since RFC:
* fix offset calculations in ramdax_{get,set}_config_data
* use a magic constant instead of a random number as nd_set->cookie*

RFC: https://lore.kernel.org/all/20250612083153.48624-1-rppt@kernel.org


Mike Rapoport (Microsoft) (1):
  nvdimm: allow exposing RAM carveouts as NVDIMM DIMM devices

 drivers/nvdimm/ramdax.c | 281 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 281 insertions(+)
 create mode 100644 drivers/nvdimm/ramdax.c


base-commit: c17b750b3ad9f45f2b6f7e6f7f4679844244f0b9
-- 
2.50.1