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Message-ID: <68b0f8a31a2b8_293b3294ae@iweiny-mobl.notmuch>
Date: Thu, 28 Aug 2025 19:47:31 -0500
From: Ira Weiny <ira.weiny@...el.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>, Michal Clapinski <mclapinski@...gle.com>
CC: <jane.chu@...cle.com>, Mike Rapoport <rppt@...nel.org>, Pasha Tatashin
<pasha.tatashin@...een.com>, Tyler Hicks <code@...icks.com>,
<linux-kernel@...r.kernel.org>, <nvdimm@...ts.linux.dev>
Subject: Re: [PATCH 1/1] nvdimm: allow exposing RAM carveouts as NVDIMM DIMM
devices
+ Michal
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.
While I recognize this driver and the e820 driver are mutually
exclusive[1][2]. I do wonder if the use cases are the same?
>From a high level I don't like the idea of adding kernel parameters. So
if this could solve Michal's problem I'm inclined to go this direction.
Ira
[1] https://lore.kernel.org/all/aExQ7nSejklEeVn0@kernel.org/
[2] https://lore.kernel.org/all/20250612114210.2786075-1-mclapinski@google.com/
>
> 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 (Mircosoft) <rppt@...nel.org>
> ---
> drivers/nvdimm/ramdax.c | 281 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 281 insertions(+)
> create mode 100644 drivers/nvdimm/ramdax.c
>
> diff --git a/drivers/nvdimm/ramdax.c b/drivers/nvdimm/ramdax.c
> new file mode 100644
> index 000000000000..27c5102f600c
> --- /dev/null
> +++ b/drivers/nvdimm/ramdax.c
> @@ -0,0 +1,281 @@
> +// 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/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);
> +
> + /* 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 = 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)
> + 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);
> +}
> +
> +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");
> --
> 2.50.1
>
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