linux-kernel - [RFC PATCH 0/1] nvdimm: allow exposing RAM as libnvdimm DIMMs

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Message-ID: <20250612083153.48624-1-rppt@kernel.org>
Date: Thu, 12 Jun 2025 11:31:52 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Dan Williams <dan.j.williams@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>
Cc: Pasha Tatashin <pasha.tatashin@...een.com>,
	Tyler Hicks <code@...icks.com>,
	linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	"Mike Rapoport (Microsoft)" <rppt@...nel.org>
Subject: [RFC PATCH 0/1] nvdimm: allow exposing RAM as libnvdimm DIMMs

From: "Mike Rapoport (Microsoft)" <rppt@...nel.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. 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.

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

 drivers/nvdimm/Kconfig  |  15 +++
 drivers/nvdimm/Makefile |   1 +
 drivers/nvdimm/ramdax.c | 279 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 295 insertions(+)
 create mode 100644 drivers/nvdimm/ramdax.c

base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
-- 
2.47.2