Message-ID: <9d75cf8a-42ae-4e61-90e9-6ddd937ddb01@oracle.com>
Date: Thu, 12 Jun 2025 14:12:42 -0700
From: jane.chu@...cle.com
To: Mike Rapoport <rppt@...nel.org>, 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
Subject: Re: [RFC PATCH 1/1] nvdimm: allow exposing RAM carveouts as NVDIMM
 DIMM devices


On 6/12/2025 1:31 AM, 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.
> 
> 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.

Just curious, how does the new driver work with Michal Clapinski's 
recent patch that adds 
"nd_e820.pmem=ss[KMG],nn[KMG][,mode=fsdax/devdax,align=aa[KMG]]" kernel 
parameter ?

thanks,
-jane

> 
> Signed-off-by: Mike Rapoport (Mircosoft) <rppt@...nel.org>
> ---
>   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
> 
> diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
> index fde3e17c836c..7aae74a29f10 100644
> --- a/drivers/nvdimm/Kconfig
> +++ b/drivers/nvdimm/Kconfig
> @@ -97,6 +97,21 @@ config OF_PMEM
>   
>   	  Select Y if unsure.
>   
> +config RAMDAX
> +	tristate "Support persistent memory interfaces on RAM carveouts"
> +	depends on OF || (X86 && X86_PMEM_LEGACY=n)
> +	select X86_PMEM_LEGACY_DEVICE
> +	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.
> +
> +	  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..67b0a240c0ae
> --- /dev/null
> +++ b/drivers/nvdimm/ramdax.c
> @@ -0,0 +1,279 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2015, 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/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);
> +
> +	/* FIXME: cleanup dimm and region devices */
> +
> +	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 = get_random_u64();
> +	nd_set->cookie2 = 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)
> +		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, buf_len);
> +
> +	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, buf_len);
> +
> +	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);
> +}
> +
> +static int ramdax_probe_of(struct platform_device *pdev,
> +			     struct nvdimm_bus *bus, struct device_node *np)
> +{
> +	int err;
> +
> +	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;
> +}
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id ramdax_of_matches[] = {
> +	{ .compatible = "pmem-region", },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, ramdax_of_matches);
> +#endif
> +
> +static struct platform_driver ramdax_driver = {
> +	.probe = ramdax_probe,
> +	.remove = ramdax_remove,
> +	.driver = {
> +		.name = "e820_pmem",
> +		.of_match_table = of_match_ptr(ramdax_of_matches),
> +	},
> +};
> +
> +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");

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