Re: [PATCH v3 13/25] cxl/region: Add sparse DAX region support

[Li, Ming4]

On 8/16/2024 10:44 PM, ira.weiny@xxxxxxxxx wrote:
> From: Navneet Singh <navneet.singh@xxxxxxxxx>
>
> Dynamic Capacity CXL regions must allow memory to be added or removed
> dynamically.  In addition to the quantity of memory available the
> location of the memory within a DC partition is dynamic based on the
> extents offered by a device.  CXL DAX regions must accommodate the
> sparseness of this memory in the management of DAX regions and devices.
>
> Introduce the concept of a sparse DAX region.  Add a create_dc_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.
>
> Sparse regions complicate the range mapping of dax devices.  There is no
> known use case for range mapping on sparse regions.  Avoid the
> complication by preventing range mapping of dax devices on sparse
> regions.
>
> Interleaving is deferred for now.  Add checks.
>
> Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> ---
> Changes:
> [Fan: use single function for dc region store]
> [djiang: avoid setting dev_size twice]
> [djbw: Check DCD support and interleave restriction on region creation]
> [iweiny: squash patch : dax/region: Prevent range mapping allocation on sparse regions]
> [iwieny: remove reviews]
> [iweiny: rebase to master]
> [iweiny: push sysfs version to 6.12]
> [iweiny: make cxled_to_mds inline]
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 22 ++++++++--------
>  drivers/cxl/core/core.h                 | 12 +++++++++
>  drivers/cxl/core/port.c                 |  1 +
>  drivers/cxl/core/region.c               | 46 +++++++++++++++++++++++++++++++--
>  drivers/dax/bus.c                       | 10 +++++++
>  drivers/dax/bus.h                       |  1 +
>  drivers/dax/cxl.c                       | 16 ++++++++++--
>  7 files changed, 93 insertions(+), 15 deletions(-)
>
[...]
> @@ -2185,8 +2191,13 @@ 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_REGION_DC &&
> +		    !cxl_dcd_supported(cxled_to_mds(cxled))) {
> +			dev_dbg(dev, "DCD unsupported\n");
> +			return -EINVAL;

need a 'goto out' here to dereference the device?


> +		}
> +		rc = attach_target(cxlr, cxled, pos, TASK_INTERRUPTIBLE);
>  out:
>  		put_device(dev);
>  	}
> @@ -2534,6 +2545,7 @@ static struct cxl_region *__create_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",
> @@ -2587,6 +2599,20 @@ 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)
> +{
> +	return create_region_store(dev, buf, len, CXL_REGION_DC);
> +}
> +DEVICE_ATTR_RW(create_dc_region);
> +
>  static ssize_t region_show(struct device *dev, struct device_attribute *attr,
>  			   char *buf)
>  {
> @@ -3168,6 +3194,11 @@ 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);
> @@ -3260,6 +3291,16 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  		return ERR_PTR(-EINVAL);
>  
>  	mode = cxl_decoder_to_region_mode(cxled->mode);
> +	if (mode == CXL_REGION_DC) {
> +		if (!cxl_dcd_supported(cxled_to_mds(cxled))) {
> +			dev_err(&cxled->cxld.dev, "DCD unsupported\n");
> +			return ERR_PTR(-EINVAL);
> +		}
> +		if (cxled->cxld.interleave_ways != 1) {
> +			dev_err(&cxled->cxld.dev, "Interleaving and DCD not supported\n");
> +			return ERR_PTR(-EINVAL);
> +		}
> +	}
>  	do {
>  		cxlr = __create_region(cxlrd, mode,
>  				       atomic_read(&cxlrd->region_id));
> @@ -3467,6 +3508,7 @@ 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 fde29e0ad68b..d8cb5195a227 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -178,6 +178,11 @@ 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);
> @@ -301,6 +306,9 @@ static unsigned long long dax_region_avail_size(struct dax_region *dax_region)
>  
>  	lockdep_assert_held(&dax_region_rwsem);
>  
> +	if (is_sparse(dax_region))
> +		return 0;
> +
>  	for_each_dax_region_resource(dax_region, res)
>  		size -= resource_size(res);
>  	return size;
> @@ -1373,6 +1381,8 @@ 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_sparse(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 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 9b29e732b39a..367e86b1c22a 100644
> --- a/drivers/dax/cxl.c
> +++ b/drivers/dax/cxl.c
> @@ -13,19 +13,31 @@ 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;
>  
> +	if (cxlr->mode == CXL_REGION_DC)
> +		/* 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,
>  	};
>  
>