Re: [PATCH 09/26] cxl/region: Add Dynamic Capacity CXL region support

Dave Jiang
2024-03-27T17:27:44Z

On 3/24/24 4:18 PM, ira.weiny@intel.com wrote:
> From: Navneet Singh <navneet.singh@intel.com>
>
> CXL devices optionally support dynamic capacity. CXL Regions must be
> configured correctly to access this capacity. Similar to ram and pmem
> partitions, DC Regions, as they are called in CXL 3.1, represent
> different partitions of the DPA space.
>
> Introduce the concept of a sparse DAX region. Add the create_dc_region
> sysfs entry to create sparse DC DAX regions. Special case DC capable
> regions to create a 0 sized seed DAX device to maintain backwards
> compatibility with older software which needs a default DAX device to
> hold the region reference.
>
> Flag sparse DAX regions to indicate 0 capacity available until such time
> as DC capacity is added.
>
> Interleaving is deferred in this series. Add an early check.
>
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> Changes for v1:
> [djiang: mark sysfs entries to be in 6.10 kernel including date]
> [djbw: change dax region typing to be 'sparse' rather than 'dynamic']
> [iweiny: rebase changes to master instead of type2 patches]
> ---
> Documentation/ABI/testing/sysfs-bus-cxl | 22 +++++++++++-----------
> drivers/cxl/core/core.h | 1 +
> drivers/cxl/core/port.c | 1 +
> drivers/cxl/core/region.c | 33 +++++++++++++++++++++++++++++++++
> drivers/dax/bus.c | 8 ++++++++
> drivers/dax/bus.h | 1 +
> drivers/dax/cxl.c | 15 +++++++++++++--
> 7 files changed, 68 insertions(+), 13 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 8a4f572c8498..f0cf52fff9fa 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -411,20 +411,20 @@ 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,dc}_region
> +Date: May, 2022, January, 2023, June 2024
> +KernelVersion: v6.0 (pmem), v6.3 (ram), v6.10 (dc)
> Contact: linux-cxl@vger.kernel.org
> 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 Capacity
> + (DC) 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

-EBUSY?

> + 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 3b64fb1b9ed0..91abeffbe985 100644
> --- a/drivers/cxl/core/core.h
> +++ b/drivers/cxl/core/core.h
> @@ -13,6 +13,7 @@ extern struct attribute_group cxl_base_attribute_group;
> #ifdef CONFIG_CXL_REGION
> 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_dc_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 036b61cb3007..661177b575f7 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -335,6 +335,7 @@ 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_dc_region)
> SET_CXL_REGION_ATTR(delete_region)
> NULL,
> };
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index ec3b8c6948e9..0d7b09a49dcf 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2205,6 +2205,7 @@ static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd,
> switch (mode) {
> case CXL_REGION_RAM:
> case CXL_REGION_PMEM:
> + case CXL_REGION_DC:
> break;
> default:
> dev_err(&cxlrd->cxlsd.cxld.dev, "unsupported mode %s\n",
> @@ -2314,6 +2315,32 @@ static ssize_t create_ram_region_store(struct device *dev,
> }
> DEVICE_ATTR_RW(create_ram_region);
>
> +static ssize_t create_dc_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_dc_region_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t len)
> +{
> + struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev);
> + struct cxl_region *cxlr;
> + int rc, id;
> +
> + rc = sscanf(buf, "region%d\n", &id);
> + if (rc != 1)
> + return -EINVAL;
> +
> + cxlr = __create_region(cxlrd, CXL_REGION_DC, id);
> + if (IS_ERR(cxlr))
> + return PTR_ERR(cxlr);
> +
> + return len;
> +}
> +DEVICE_ATTR_RW(create_dc_region);
> +
> static ssize_t region_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> {
> @@ -2759,6 +2786,11 @@ static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
> struct device *dev;
> int rc;
>
> + if (cxlr->mode == CXL_REGION_DC && cxlr->params.interleave_ways != 1) {
> + dev_err(&cxlr->dev, "Interleaving DC not supported\n");
> + return -EINVAL;
> + }
> +
> cxlr_dax = cxl_dax_region_alloc(cxlr);
> if (IS_ERR(cxlr_dax))
> return PTR_ERR(cxlr_dax);
> @@ -3040,6 +3072,7 @@ static int cxl_region_probe(struct device *dev)
> case CXL_REGION_PMEM:
> return devm_cxl_add_pmem_region(cxlr);
> case CXL_REGION_RAM:
> + case CXL_REGION_DC:
> /*
> * The region can not be manged by CXL if any portion of
> * it is already online as 'System RAM'
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index cb148f74ceda..903566aff5eb 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -181,6 +181,11 @@ static bool is_static(struct dax_region *dax_region)
> return (dax_region->res.flags & IORESOURCE_DAX_STATIC) != 0;
> }
>
> +static bool is_sparse(struct dax_region *dax_region)
> +{
> + return (dax_region->res.flags & IORESOURCE_DAX_SPARSE_CAP) != 0;
> +}
> +
> bool static_dev_dax(struct dev_dax *dev_dax)
> {
> return is_static(dev_dax->region);
> @@ -304,6 +309,9 @@ static unsigned long long dax_region_avail_size(struct dax_region *dax_region)
>
> WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
>
> + if (is_sparse(dax_region))
> + return 0;
> +
> for_each_dax_region_resource(dax_region, res)
> size -= resource_size(res);
> return size;
> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
> index cbbf64443098..783bfeef42cc 100644
> --- a/drivers/dax/bus.h
> +++ b/drivers/dax/bus.h
> @@ -13,6 +13,7 @@ struct dax_region;
> /* dax bus specific ioresource flags */
> #define IORESOURCE_DAX_STATIC BIT(0)
> #define IORESOURCE_DAX_KMEM BIT(1)
> +#define IORESOURCE_DAX_SPARSE_CAP 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 c696837ab23c..415d03fbf9b6 100644
> --- a/drivers/dax/cxl.c
> +++ b/drivers/dax/cxl.c
> @@ -13,19 +13,30 @@ 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);
>
> + flags = IORESOURCE_DAX_KMEM;
> + if (cxlr->mode == CXL_REGION_DC)
> + flags |= IORESOURCE_DAX_SPARSE_CAP;
> +
> 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;
>
> + dev_size = range_len(&cxlr_dax->hpa_range);
> + /* Add empty seed dax device */
> + if (cxlr->mode == CXL_REGION_DC)
> + dev_size = 0;

Nit. Just do if/else so dev_size isn't set twice if mode is DC.

> +
> 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,
> };
>
>