On 6/25/26 4:04 AM, Anisa Su wrote:
> From: Ira Weiny <[email protected]>
>
> DC DAX regions must allow memory to be added or removed dynamically.
> In addition to the quantity of memory available the,
stray comma
DJ
> location of the memory within a DC partition is dynamic, based on the
> extents offered by a device. CXL DAX regions must accommodate the
> dynamic movement of this memory in the management of DAX regions and devices.
>
> Introduce the concept of a dynamic DAX region. Introduce
> create_dynamic_ram_1_region() sysfs entry to create such regions.
> Special case DC-capable regions to create a 0 sized seed DAX device
> to maintain compatibility which requires a default DAX device to hold a
> region reference.
>
> Indicate 0 byte available capacity until such time that capacity is
> added.
>
> Dynamic regions complicate the range mapping of dax devices. There is no
> known use case for range mapping on dynamic regions. Avoid the
> complication by preventing range mapping of dax devices on dynamic
> regions.
>
> Interleaving is deferred for now. Add checks.
>
> Based on an original patch by Navneet Singh.
>
> Signed-off-by: Ira Weiny <[email protected]>
> Signed-off-by: Anisa Su <[email protected]>
>
> ---
> Changes:
> 1. Documentation: bump kver to 7.3 and date to June 2026
> 2. port.c: use helper function to_cxl_memdev_state() in cxled_to_mds()
> 3. region.c: cxled_to_mds() can return NULL with ^ above change.
> Handle properly in store_targetN()
> 4. port.c: check if the root decoder supports ram regions before
> exposing create_dynamic_ram_1_region attribute in
> cxl_root_decoder_visible()
> 5. Rename dynamic_ram_a to dynamic_ram_1
> 6. Add dynamic_ram_1 to mode_show()
> ---
> Documentation/ABI/testing/sysfs-bus-cxl | 22 ++++++-------
> drivers/cxl/core/core.h | 9 ++++++
> drivers/cxl/core/port.c | 5 +++
> drivers/cxl/core/region.c | 43 +++++++++++++++++++++++--
> drivers/cxl/core/region_dax.c | 6 ++++
> drivers/dax/bus.c | 10 ++++++
> drivers/dax/bus.h | 1 +
> drivers/dax/cxl.c | 17 ++++++++--
> 8 files changed, 98 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl
> b/Documentation/ABI/testing/sysfs-bus-cxl
> index 499741cbb899..00b98bbe0ff3 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -434,20 +434,20 @@ Description:
> interleave_granularity).
>
>
> -What: /sys/bus/cxl/devices/decoderX.Y/create_{pmem,ram}_region
> -Date: May, 2022, January, 2023
> -KernelVersion: v6.0 (pmem), v6.3 (ram)
> +What:
> /sys/bus/cxl/devices/decoderX.Y/create_{pmem,ram,dynamic_ram_1}_region
> +Date: May, 2022, January, 2023, June 2026
> +KernelVersion: v6.0 (pmem), v6.3 (ram), v7.3 (dynamic_ram_1)
> Contact: [email protected]
> Description:
> (RW) Write a string in the form 'regionZ' to start the process
> - of defining a new persistent, or volatile memory region
> - (interleave-set) within the decode range bounded by root decoder
> - 'decoderX.Y'. The value written must match the current value
> - returned from reading this attribute. An atomic compare exchange
> - operation is done on write to assign the requested id to a
> - region and allocate the region-id for the next creation attempt.
> - EBUSY is returned if the region name written does not match the
> - current cached value.
> + of defining a new persistent, volatile, or dynamic RAM memory
> + region (interleave-set) within the decode range bounded by root
> + decoder 'decoderX.Y'. The value written must match the current
> + value returned from reading this attribute. An atomic compare
> + exchange operation is done on write to assign the requested id
> + to a region and allocate the region-id for the next creation
> + attempt. EBUSY is returned if the region name written does not
> + match the current cached value.
>
>
> What: /sys/bus/cxl/devices/decoderX.Y/delete_region
> diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
> index 82ca3a476708..9ed141fa1334 100644
> --- a/drivers/cxl/core/core.h
> +++ b/drivers/cxl/core/core.h
> @@ -6,6 +6,7 @@
>
> #include <cxl/mailbox.h>
> #include <linux/rwsem.h>
> +#include <cxlmem.h>
>
> extern const struct device_type cxl_nvdimm_bridge_type;
> extern const struct device_type cxl_nvdimm_type;
> @@ -18,6 +19,13 @@ enum cxl_detach_mode {
> DETACH_INVALIDATE,
> };
>
> +static inline struct cxl_memdev_state *
> +cxled_to_mds(struct cxl_endpoint_decoder *cxled)
> +{
> + struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> + return to_cxl_memdev_state(cxlmd->cxlds);
> +}
> +
> #ifdef CONFIG_CXL_REGION
>
> struct cxl_region_context {
> @@ -29,6 +37,7 @@ struct cxl_region_context {
>
> extern struct device_attribute dev_attr_create_pmem_region;
> extern struct device_attribute dev_attr_create_ram_region;
> +extern struct device_attribute dev_attr_create_dynamic_ram_1_region;
> extern struct device_attribute dev_attr_delete_region;
> extern struct device_attribute dev_attr_region;
> extern const struct device_type cxl_pmem_region_type;
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 57d0fc72023f..279279f544d8 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -337,6 +337,7 @@ static struct attribute *cxl_decoder_root_attrs[] = {
> &dev_attr_qos_class.attr,
> SET_CXL_REGION_ATTR(create_pmem_region)
> SET_CXL_REGION_ATTR(create_ram_region)
> + SET_CXL_REGION_ATTR(create_dynamic_ram_1_region)
> SET_CXL_REGION_ATTR(delete_region)
> NULL,
> };
> @@ -366,6 +367,10 @@ static umode_t cxl_root_decoder_visible(struct kobject
> *kobj, struct attribute *
> if (a == CXL_REGION_ATTR(create_ram_region) && !can_create_ram(cxlrd))
> return 0;
>
> + if (a == CXL_REGION_ATTR(create_dynamic_ram_1_region) &&
> + !can_create_ram(cxlrd))
> + return 0;
> +
> if (a == CXL_REGION_ATTR(delete_region) &&
> !(can_create_pmem(cxlrd) || can_create_ram(cxlrd)))
> return 0;
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index e50dc716d4e8..ba03ec5e27c3 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -493,6 +493,11 @@ static int set_interleave_ways(struct cxl_region *cxlr,
> int val)
> int save, rc;
> u8 iw;
>
> + if (cxlr->mode == CXL_PARTMODE_DYNAMIC_RAM_1 && val != 1) {
> + dev_err(&cxlr->dev, "Interleaving and DCD not supported\n");
> + return -EINVAL;
> + }
> +
> rc = ways_to_eiw(val, &iw);
> if (rc)
> return rc;
> @@ -642,6 +647,8 @@ static ssize_t mode_show(struct device *dev, struct
> device_attribute *attr,
> desc = "ram";
> else if (cxlr->mode == CXL_PARTMODE_PMEM)
> desc = "pmem";
> + else if (cxlr->mode == CXL_PARTMODE_DYNAMIC_RAM_1)
> + desc = "dynamic_ram_1";
> else
> desc = "";
>
> @@ -2389,6 +2396,8 @@ static size_t store_targetN(struct cxl_region *cxlr,
> const char *buf, int pos,
> if (sysfs_streq(buf, "\n"))
> rc = detach_target(cxlr, pos);
> else {
> + struct cxl_endpoint_decoder *cxled;
> + struct cxl_memdev_state *mds;
> struct device *dev;
>
> dev = bus_find_device_by_name(&cxl_bus_type, NULL, buf);
> @@ -2400,8 +2409,21 @@ static size_t store_targetN(struct cxl_region *cxlr,
> const char *buf, int pos,
> goto out;
> }
>
> - rc = attach_target(cxlr, to_cxl_endpoint_decoder(dev), pos,
> - TASK_INTERRUPTIBLE);
> + cxled = to_cxl_endpoint_decoder(dev);
> + if (cxlr->mode == CXL_PARTMODE_DYNAMIC_RAM_1) {
> + mds = cxled_to_mds(cxled);
> + if (!mds) {
> + dev_dbg(dev, "No memdev state\n");
> + rc = -ENODEV;
> + goto out;
> + }
> + if (!cxl_dcd_supported(mds)) {
> + dev_dbg(dev, "DCD unsupported\n");
> + rc = -EINVAL;
> + goto out;
> + }
> + }
> + rc = attach_target(cxlr, cxled, pos, TASK_INTERRUPTIBLE);
> out:
> put_device(dev);
> }
> @@ -2750,6 +2772,7 @@ static struct cxl_region *__create_region(struct
> cxl_root_decoder *cxlrd,
> switch (mode) {
> case CXL_PARTMODE_RAM:
> case CXL_PARTMODE_PMEM:
> + case CXL_PARTMODE_DYNAMIC_RAM_1:
> break;
> default:
> dev_err(&cxlrd->cxlsd.cxld.dev, "unsupported mode %d\n", mode);
> @@ -2802,6 +2825,21 @@ static ssize_t create_ram_region_store(struct device
> *dev,
> }
> DEVICE_ATTR_RW(create_ram_region);
>
> +static ssize_t create_dynamic_ram_1_region_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + return __create_region_show(to_cxl_root_decoder(dev), buf);
> +}
> +
> +static ssize_t create_dynamic_ram_1_region_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t len)
> +{
> + return create_region_store(dev, buf, len, CXL_PARTMODE_DYNAMIC_RAM_1);
> +}
> +DEVICE_ATTR_RW(create_dynamic_ram_1_region);
> +
> static ssize_t region_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> {
> @@ -4083,6 +4121,7 @@ static int cxl_region_probe(struct device *dev)
>
> return devm_cxl_add_pmem_region(cxlr);
> case CXL_PARTMODE_RAM:
> + case CXL_PARTMODE_DYNAMIC_RAM_1:
> rc = devm_cxl_region_edac_register(cxlr);
> if (rc)
> dev_dbg(&cxlr->dev, "CXL EDAC registration for
> region_id=%d failed\n",
> diff --git a/drivers/cxl/core/region_dax.c b/drivers/cxl/core/region_dax.c
> index de04f78f6ad8..3865961c4301 100644
> --- a/drivers/cxl/core/region_dax.c
> +++ b/drivers/cxl/core/region_dax.c
> @@ -84,6 +84,12 @@ int devm_cxl_add_dax_region(struct cxl_region *cxlr)
> struct device *dev;
> int rc;
>
> + if (cxlr->mode == CXL_PARTMODE_DYNAMIC_RAM_1 &&
> + cxlr->params.interleave_ways != 1) {
> + dev_err(&cxlr->dev, "Interleaving DC not supported\n");
> + return -EINVAL;
> + }
> +
> struct cxl_dax_region *cxlr_dax __free(put_cxl_dax_region) =
> cxl_dax_region_alloc(cxlr);
> if (IS_ERR(cxlr_dax))
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index ccfe65004888..7356aaaffe57 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -177,6 +177,11 @@ static bool is_static(struct dax_region *dax_region)
> return (dax_region->res.flags & IORESOURCE_DAX_STATIC) != 0;
> }
>
> +static bool is_dynamic(struct dax_region *dax_region)
> +{
> + return (dax_region->res.flags & IORESOURCE_DAX_DCD) != 0;
> +}
> +
> bool static_dev_dax(struct dev_dax *dev_dax)
> {
> return is_static(dev_dax->region);
> @@ -300,6 +305,9 @@ static unsigned long long dax_region_avail_size(struct
> dax_region *dax_region)
>
> lockdep_assert_held(&dax_region_rwsem);
>
> + if (is_dynamic(dax_region))
> + return 0;
> +
> for_each_dax_region_resource(dax_region, res)
> size -= resource_size(res);
> return size;
> @@ -1385,6 +1393,8 @@ static umode_t dev_dax_visible(struct kobject *kobj,
> struct attribute *a, int n)
> return 0;
> if (a == &dev_attr_mapping.attr && is_static(dax_region))
> return 0;
> + if (a == &dev_attr_mapping.attr && is_dynamic(dax_region))
> + return 0;
> if ((a == &dev_attr_align.attr ||
> a == &dev_attr_size.attr) && is_static(dax_region))
> return 0444;
> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
> index 5909171a4428..6e739bfab932 100644
> --- a/drivers/dax/bus.h
> +++ b/drivers/dax/bus.h
> @@ -15,6 +15,7 @@ struct dax_region;
> /* dax bus specific ioresource flags */
> #define IORESOURCE_DAX_STATIC BIT(0)
> #define IORESOURCE_DAX_KMEM BIT(1)
> +#define IORESOURCE_DAX_DCD BIT(2)
>
> struct dax_region *alloc_dax_region(struct device *parent, int region_id,
> struct range *range, int target_node, unsigned int align,
> diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
> index 3ab39b77843d..cedd974c2d0c 100644
> --- a/drivers/dax/cxl.c
> +++ b/drivers/dax/cxl.c
> @@ -13,19 +13,32 @@ static int cxl_dax_region_probe(struct device *dev)
> struct cxl_region *cxlr = cxlr_dax->cxlr;
> struct dax_region *dax_region;
> struct dev_dax_data data;
> + resource_size_t dev_size;
> + unsigned long flags;
>
> if (nid == NUMA_NO_NODE)
> nid = memory_add_physaddr_to_nid(cxlr_dax->hpa_range.start);
>
> + if (cxlr->mode == CXL_PARTMODE_DYNAMIC_RAM_1)
> + flags = IORESOURCE_DAX_DCD;
> + else
> + flags = IORESOURCE_DAX_KMEM;
> +
> dax_region = alloc_dax_region(dev, cxlr->id, &cxlr_dax->hpa_range, nid,
> - PMD_SIZE, IORESOURCE_DAX_KMEM);
> + PMD_SIZE, flags);
> if (!dax_region)
> return -ENOMEM;
>
> + if (cxlr->mode == CXL_PARTMODE_DYNAMIC_RAM_1)
> + /* Add empty seed dax device */
> + dev_size = 0;
> + else
> + dev_size = range_len(&cxlr_dax->hpa_range);
> +
> data = (struct dev_dax_data) {
> .dax_region = dax_region,
> .id = -1,
> - .size = range_len(&cxlr_dax->hpa_range),
> + .size = dev_size,
> .memmap_on_memory = true,
> };
>
