Message-ID: <aQj0rV6R_KCgzr42@kernel.org>
Date: Mon, 3 Nov 2025 20:30:05 +0200
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: jane.chu@...cle.com,
	Michał Cłapiński <mclapinski@...gle.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Tyler Hicks <code@...icks.com>, linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev
Subject: Re: [PATCH v3 1/1] nvdimm: allow exposing RAM carveouts as NVDIMM
 DIMM devices

Gentle ping?

On Sun, Oct 26, 2025 at 05:38:41PM +0200, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> There are use cases, for example virtual machine hosts, that create
> "persistent" memory regions using memmap= option on x86 or dummy
> pmem-region device tree nodes on DT based systems.
> 
> Both these options are inflexible because they create static regions and
> the layout of the "persistent" memory cannot be adjusted without reboot
> and sometimes they even require firmware update.
> 
> Add a ramdax driver that allows creation of DIMM devices on top of
> E820_TYPE_PRAM regions and devicetree pmem-region nodes.
> 
> The DIMMs support label space management on the "device" and provide a
> flexible way to access RAM using fsdax and devdax.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  drivers/nvdimm/Kconfig  |  19 +++
>  drivers/nvdimm/Makefile |   1 +
>  drivers/nvdimm/ramdax.c | 282 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 302 insertions(+)
>  create mode 100644 drivers/nvdimm/ramdax.c
> 
> diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
> index fde3e17c836c..44ab929a1ad5 100644
> --- a/drivers/nvdimm/Kconfig
> +++ b/drivers/nvdimm/Kconfig
> @@ -97,6 +97,25 @@ config OF_PMEM
>  
>  	  Select Y if unsure.
>  
> +config RAMDAX
> +	tristate "Support persistent memory interfaces on RAM carveouts"
> +	depends on X86_PMEM_LEGACY || OF || COMPILE_TEST
> +	default LIBNVDIMM
> +	help
> +	  Allows creation of DAX devices on RAM carveouts.
> +
> +	  Memory ranges that are manually specified by the
> +	  'memmap=nn[KMG]!ss[KMG]' kernel command line or defined by dummy
> +	  pmem-region device tree nodes would be managed by this driver as DIMM
> +	  devices with support for dynamic layout of namespaces.
> +	  The driver steals 128K in the end of the memmap range for the
> +	  namespace management. This allows supporting up to 509 namespaces
> +	  (see 'ndctl create-namespace --help').
> +	  The driver should be force bound to e820_pmem or pmem-region platform
> +	  devices using 'driver_override' device attribute.
> +
> +	  Select N if unsure.
> +
>  config NVDIMM_KEYS
>  	def_bool y
>  	depends on ENCRYPTED_KEYS
> diff --git a/drivers/nvdimm/Makefile b/drivers/nvdimm/Makefile
> index ba0296dca9db..8c268814936c 100644
> --- a/drivers/nvdimm/Makefile
> +++ b/drivers/nvdimm/Makefile
> @@ -5,6 +5,7 @@ obj-$(CONFIG_ND_BTT) += nd_btt.o
>  obj-$(CONFIG_X86_PMEM_LEGACY) += nd_e820.o
>  obj-$(CONFIG_OF_PMEM) += of_pmem.o
>  obj-$(CONFIG_VIRTIO_PMEM) += virtio_pmem.o nd_virtio.o
> +obj-$(CONFIG_RAMDAX) += ramdax.o
>  
>  nd_pmem-y := pmem.o
>  
> diff --git a/drivers/nvdimm/ramdax.c b/drivers/nvdimm/ramdax.c
> new file mode 100644
> index 000000000000..63cf05791829
> --- /dev/null
> +++ b/drivers/nvdimm/ramdax.c
> @@ -0,0 +1,282 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2025, Mike Rapoport, Microsoft
> + *
> + * Based on e820 pmem driver:
> + * Copyright (c) 2015, Christoph Hellwig.
> + * Copyright (c) 2015, Intel Corporation.
> + */
> +#include <linux/platform_device.h>
> +#include <linux/memory_hotplug.h>
> +#include <linux/libnvdimm.h>
> +#include <linux/module.h>
> +#include <linux/numa.h>
> +#include <linux/slab.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +
> +#include <uapi/linux/ndctl.h>
> +
> +#define LABEL_AREA_SIZE	SZ_128K
> +
> +struct ramdax_dimm {
> +	struct nvdimm *nvdimm;
> +	void *label_area;
> +};
> +
> +static void ramdax_remove(struct platform_device *pdev)
> +{
> +	struct nvdimm_bus *nvdimm_bus = platform_get_drvdata(pdev);
> +
> +	nvdimm_bus_unregister(nvdimm_bus);
> +}
> +
> +static int ramdax_register_region(struct resource *res,
> +		struct nvdimm *nvdimm,
> +		struct nvdimm_bus *nvdimm_bus)
> +{
> +	struct nd_mapping_desc mapping;
> +	struct nd_region_desc ndr_desc;
> +	struct nd_interleave_set *nd_set;
> +	int nid = phys_to_target_node(res->start);
> +
> +	nd_set = kzalloc(sizeof(*nd_set), GFP_KERNEL);
> +	if (!nd_set)
> +		return -ENOMEM;
> +
> +	nd_set->cookie1 = 0xcafebeefcafebeef;
> +	nd_set->cookie2 = nd_set->cookie1;
> +	nd_set->altcookie = nd_set->cookie1;
> +
> +	memset(&mapping, 0, sizeof(mapping));
> +	mapping.nvdimm = nvdimm;
> +	mapping.start = 0;
> +	mapping.size = resource_size(res) - LABEL_AREA_SIZE;
> +
> +	memset(&ndr_desc, 0, sizeof(ndr_desc));
> +	ndr_desc.res = res;
> +	ndr_desc.numa_node = numa_map_to_online_node(nid);
> +	ndr_desc.target_node = nid;
> +	ndr_desc.num_mappings = 1;
> +	ndr_desc.mapping = &mapping;
> +	ndr_desc.nd_set = nd_set;
> +
> +	if (!nvdimm_pmem_region_create(nvdimm_bus, &ndr_desc))
> +		goto err_free_nd_set;
> +
> +	return 0;
> +
> +err_free_nd_set:
> +	kfree(nd_set);
> +	return -ENXIO;
> +}
> +
> +static int ramdax_register_dimm(struct resource *res, void *data)
> +{
> +	resource_size_t start = res->start;
> +	resource_size_t size = resource_size(res);
> +	unsigned long flags = 0, cmd_mask = 0;
> +	struct nvdimm_bus *nvdimm_bus = data;
> +	struct ramdax_dimm *dimm;
> +	int err;
> +
> +	dimm = kzalloc(sizeof(*dimm), GFP_KERNEL);
> +	if (!dimm)
> +		return -ENOMEM;
> +
> +	dimm->label_area = memremap(start + size - LABEL_AREA_SIZE,
> +				    LABEL_AREA_SIZE, MEMREMAP_WB);
> +	if (!dimm->label_area) {
> +		err = -ENOMEM;
> +		goto err_free_dimm;
> +	}
> +
> +	set_bit(NDD_LABELING, &flags);
> +	set_bit(NDD_REGISTER_SYNC, &flags);
> +	set_bit(ND_CMD_GET_CONFIG_SIZE, &cmd_mask);
> +	set_bit(ND_CMD_GET_CONFIG_DATA, &cmd_mask);
> +	set_bit(ND_CMD_SET_CONFIG_DATA, &cmd_mask);
> +	dimm->nvdimm = nvdimm_create(nvdimm_bus, dimm,
> +				     /* dimm_attribute_groups */ NULL,
> +				     flags, cmd_mask, 0, NULL);
> +	if (!dimm->nvdimm) {
> +		err = -ENOMEM;
> +		goto err_unmap_label;
> +	}
> +
> +	err = ramdax_register_region(res, dimm->nvdimm, nvdimm_bus);
> +	if (err)
> +		goto err_remove_nvdimm;
> +
> +	return 0;
> +
> +err_remove_nvdimm:
> +	nvdimm_delete(dimm->nvdimm);
> +err_unmap_label:
> +	memunmap(dimm->label_area);
> +err_free_dimm:
> +	kfree(dimm);
> +	return err;
> +}
> +
> +static int ramdax_get_config_size(struct nvdimm *nvdimm, int buf_len,
> +		struct nd_cmd_get_config_size *cmd)
> +{
> +	if (sizeof(*cmd) > buf_len)
> +		return -EINVAL;
> +
> +	*cmd = (struct nd_cmd_get_config_size){
> +		.status = 0,
> +		.config_size = LABEL_AREA_SIZE,
> +		.max_xfer = 8,
> +	};
> +
> +	return 0;
> +}
> +
> +static int ramdax_get_config_data(struct nvdimm *nvdimm, int buf_len,
> +		struct nd_cmd_get_config_data_hdr *cmd)
> +{
> +	struct ramdax_dimm *dimm = nvdimm_provider_data(nvdimm);
> +
> +	if (sizeof(*cmd) > buf_len)
> +		return -EINVAL;
> +	if (struct_size(cmd, out_buf, cmd->in_length) > buf_len)
> +		return -EINVAL;
> +	if (cmd->in_offset + cmd->in_length > LABEL_AREA_SIZE)
> +		return -EINVAL;
> +
> +	memcpy(cmd->out_buf, dimm->label_area + cmd->in_offset, cmd->in_length);
> +
> +	return 0;
> +}
> +
> +static int ramdax_set_config_data(struct nvdimm *nvdimm, int buf_len,
> +		struct nd_cmd_set_config_hdr *cmd)
> +{
> +	struct ramdax_dimm *dimm = nvdimm_provider_data(nvdimm);
> +
> +	if (sizeof(*cmd) > buf_len)
> +		return -EINVAL;
> +	if (struct_size(cmd, in_buf, cmd->in_length) > buf_len)
> +		return -EINVAL;
> +	if (cmd->in_offset + cmd->in_length > LABEL_AREA_SIZE)
> +		return -EINVAL;
> +
> +	memcpy(dimm->label_area + cmd->in_offset, cmd->in_buf, cmd->in_length);
> +
> +	return 0;
> +}
> +
> +static int ramdax_nvdimm_ctl(struct nvdimm *nvdimm, unsigned int cmd,
> +		void *buf, unsigned int buf_len)
> +{
> +	unsigned long cmd_mask = nvdimm_cmd_mask(nvdimm);
> +
> +	if (!test_bit(cmd, &cmd_mask))
> +		return -ENOTTY;
> +
> +	switch (cmd) {
> +	case ND_CMD_GET_CONFIG_SIZE:
> +		return ramdax_get_config_size(nvdimm, buf_len, buf);
> +	case ND_CMD_GET_CONFIG_DATA:
> +		return ramdax_get_config_data(nvdimm, buf_len, buf);
> +	case ND_CMD_SET_CONFIG_DATA:
> +		return ramdax_set_config_data(nvdimm, buf_len, buf);
> +	default:
> +		return -ENOTTY;
> +	}
> +}
> +
> +static int ramdax_ctl(struct nvdimm_bus_descriptor *nd_desc,
> +		struct nvdimm *nvdimm, unsigned int cmd, void *buf,
> +		unsigned int buf_len, int *cmd_rc)
> +{
> +	/*
> +	 * No firmware response to translate, let the transport error
> +	 * code take precedence.
> +	 */
> +	*cmd_rc = 0;
> +
> +	if (!nvdimm)
> +		return -ENOTTY;
> +	return ramdax_nvdimm_ctl(nvdimm, cmd, buf, buf_len);
> +}
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id ramdax_of_matches[] = {
> +	{ .compatible = "pmem-region", },
> +	{ },
> +};
> +#endif
> +
> +static int ramdax_probe_of(struct platform_device *pdev,
> +		struct nvdimm_bus *bus, struct device_node *np)
> +{
> +	int err;
> +
> +	if (!of_match_node(ramdax_of_matches, np))
> +		return -ENODEV;
> +
> +	for (int i = 0; i < pdev->num_resources; i++) {
> +		err = ramdax_register_dimm(&pdev->resource[i], bus);
> +		if (err)
> +			goto err_unregister;
> +	}
> +
> +	return 0;
> +
> +err_unregister:
> +	/*
> +	 * FIXME: should we unregister the dimms that were registered
> +	 * successfully
> +	 */
> +	return err;
> +}
> +
> +static int ramdax_probe(struct platform_device *pdev)
> +{
> +	static struct nvdimm_bus_descriptor nd_desc;
> +	struct device *dev = &pdev->dev;
> +	struct nvdimm_bus *nvdimm_bus;
> +	struct device_node *np;
> +	int rc = -ENXIO;
> +
> +	nd_desc.provider_name = "ramdax";
> +	nd_desc.module = THIS_MODULE;
> +	nd_desc.ndctl = ramdax_ctl;
> +	nvdimm_bus = nvdimm_bus_register(dev, &nd_desc);
> +	if (!nvdimm_bus)
> +		goto err;
> +
> +	np = dev_of_node(&pdev->dev);
> +	if (np)
> +		rc = ramdax_probe_of(pdev, nvdimm_bus, np);
> +	else
> +		rc = walk_iomem_res_desc(IORES_DESC_PERSISTENT_MEMORY_LEGACY,
> +					 IORESOURCE_MEM, 0, -1, nvdimm_bus,
> +					 ramdax_register_dimm);
> +	if (rc)
> +		goto err;
> +
> +	platform_set_drvdata(pdev, nvdimm_bus);
> +
> +	return 0;
> +err:
> +	nvdimm_bus_unregister(nvdimm_bus);
> +	return rc;
> +}
> +
> +static struct platform_driver ramdax_driver = {
> +	.probe = ramdax_probe,
> +	.remove = ramdax_remove,
> +	.driver = {
> +		.name = "ramdax",
> +	},
> +};
> +
> +module_platform_driver(ramdax_driver);
> +
> +MODULE_DESCRIPTION("NVDIMM support for e820 type-12 memory and OF pmem-region");
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Microsoft Corporation");
> -- 
> 2.50.1
> 

-- 
Sincerely yours,
Mike.

Powered by blists - more mailing lists