Re: [PATCH v23 19/22] cxl: Allow region creation by type2 drivers

[Alejandro Lucero Palau <alucerop@amd.com>]

On 2/11/26 22:11, Cheatham, Benjamin wrote:
> On 2/1/2026 9:54 AM, alejandro.lucero-palau@amd.com wrote:
>> From: Alejandro Lucero <alucerop@amd.com>
>>
>> Creating a CXL region requires userspace intervention through the cxl
>> sysfs files. Type2 support should allow accelerator drivers to create
>> such cxl region from kernel code.
>>
>> Adding that functionality and integrating it with current support for
>> memory expanders.
>>
>> Based on https://lore.kernel.org/linux-cxl/168592159835.1948938.1647215579839222774.stgit@dwillia2-xfh.jf.intel.com/
>>
>> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
>> ---
>>   drivers/cxl/core/region.c | 131 ++++++++++++++++++++++++++++++++++++--
>>   include/cxl/cxl.h         |   3 +
>>   2 files changed, 127 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 63c2aeb2ee1f..293e63dfef22 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -2944,6 +2944,14 @@ cxl_find_region_by_name(struct cxl_root_decoder *cxlrd, const char *name)
>>   	return to_cxl_region(region_dev);
>>   }
>>   
>> +static void drop_region(struct cxl_region *cxlr)
>> +{
>> +	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
>> +	struct cxl_port *port = cxlrd_to_port(cxlrd);
>> +
>> +	devm_release_action(port->uport_dev, __unregister_region, cxlr);
>> +}
>> +
>>   static ssize_t delete_region_store(struct device *dev,
>>   				   struct device_attribute *attr,
>>   				   const char *buf, size_t len)
>> @@ -4047,14 +4055,12 @@ static int __construct_region(struct cxl_region *cxlr,
>>   	return 0;
>>   }
>>   
>> -/* Establish an empty region covering the given HPA range */
>> -static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>> -					   struct cxl_endpoint_decoder *cxled)
>> +static struct cxl_region *construct_region_begin(struct cxl_root_decoder *cxlrd,
>> +						 struct cxl_endpoint_decoder *cxled)
>>   {
>>   	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
>> -	struct cxl_port *port = cxlrd_to_port(cxlrd);
>>   	struct cxl_dev_state *cxlds = cxlmd->cxlds;
>> -	int rc, part = READ_ONCE(cxled->part);
>> +	int part = READ_ONCE(cxled->part);
>>   	struct cxl_region *cxlr;
>>   
>>   	do {
>> @@ -4063,13 +4069,26 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>>   				       cxled->cxld.target_type);
>>   	} while (IS_ERR(cxlr) && PTR_ERR(cxlr) == -EBUSY);
>>   
>> -	if (IS_ERR(cxlr)) {
>> +	if (IS_ERR(cxlr))
>>   		dev_err(cxlmd->dev.parent,
>>   			"%s:%s: %s failed assign region: %ld\n",
>>   			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
>>   			__func__, PTR_ERR(cxlr));
>> +
>> +	return cxlr;
>> +}
>> +
>> +/* Establish an empty region covering the given HPA range */
>> +static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>> +					   struct cxl_endpoint_decoder *cxled)
>> +{
>> +	struct cxl_port *port = cxlrd_to_port(cxlrd);
>> +	struct cxl_region *cxlr;
>> +	int rc;
>> +
>> +	cxlr = construct_region_begin(cxlrd, cxled);
>> +	if (IS_ERR(cxlr))
>>   		return cxlr;
>> -	}
>>   
>>   	rc = __construct_region(cxlr, cxlrd, cxled);
>>   	if (rc) {
>> @@ -4080,6 +4099,104 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>>   	return cxlr;
>>   }
>>   
>> +DEFINE_FREE(cxl_region_drop, struct cxl_region *, if (_T) drop_region(_T))
> This needs to be "if (!IS_ERR_OR_NULL(_T) drop_region(_T)". If construct_region_begin() returns an
> error pointer, drop_region() will be called with it as of now leading to a garbage pointer deref.


That's true. I will fix it.


Thank you!


>> +
>> +static struct cxl_region *
>> +__construct_new_region(struct cxl_root_decoder *cxlrd,
>> +		       struct cxl_endpoint_decoder **cxled, int ways)
>> +{
>> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled[0]);
>> +	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
>> +	struct cxl_region_params *p;
>> +	resource_size_t size = 0;
>> +	int rc, i;
>> +
>> +	struct cxl_region *cxlr __free(cxl_region_drop) =
>> +		construct_region_begin(cxlrd, cxled[0]);
>> +	if (IS_ERR(cxlr))
>> +		return cxlr;
>> +
>> +	guard(rwsem_write)(&cxl_rwsem.region);
>> +
>> +	/*
>> +	 * Sanity check. This should not happen with an accel driver handling
>> +	 * the region creation.
>> +	 */
>> +	p = &cxlr->params;
>> +	if (p->state >= CXL_CONFIG_INTERLEAVE_ACTIVE) {
>> +		dev_err(cxlmd->dev.parent,
>> +			"%s:%s: %s  unexpected region state\n",
>> +			dev_name(&cxlmd->dev), dev_name(&cxled[0]->cxld.dev),
>> +			__func__);
>> +		return ERR_PTR(-EBUSY);
>> +	}
>> +
>> +	rc = set_interleave_ways(cxlr, ways);
>> +	if (rc)
>> +		return ERR_PTR(rc);
>> +
>> +	rc = set_interleave_granularity(cxlr, cxld->interleave_granularity);
>> +	if (rc)
>> +		return ERR_PTR(rc);
>> +
>> +	scoped_guard(rwsem_read, &cxl_rwsem.dpa) {
>> +		for (i = 0; i < ways; i++) {
>> +			if (!cxled[i]->dpa_res)
>> +				return ERR_PTR(-EINVAL);
>> +			size += resource_size(cxled[i]->dpa_res);
>> +		}
>> +
>> +		rc = alloc_hpa(cxlr, size);
>> +		if (rc)
>> +			return ERR_PTR(rc);
>> +
>> +		for (i = 0; i < ways; i++) {
>> +			rc = cxl_region_attach(cxlr, cxled[i], 0);
> Position parameter is hardcoded to 0. It should be set to i, right? This kind of goes back to my
> issues in patch 12/22; the interleaving functionality is there but it looks unused.
>
>> +			if (rc)
>> +				return ERR_PTR(rc);
>> +		}
>> +	}
>> +
>> +	rc = cxl_region_decode_commit(cxlr);
>> +	if (rc)
>> +		return ERR_PTR(rc);
>> +
>> +	p->state = CXL_CONFIG_COMMIT;
>> +
>> +	return no_free_ptr(cxlr);
>> +}
>> +
>> +/**
>> + * cxl_create_region - Establish a region given an endpoint decoder
>> + * @cxlrd: root decoder to allocate HPA
>> + * @cxled: endpoint decoders with reserved DPA capacity
>> + * @ways: interleave ways required
>> + *
>> + * Returns a fully formed region in the commit state and attached to the
>> + * cxl_region driver.
>> + */
>> +struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>> +				     struct cxl_endpoint_decoder **cxled,
>> +				     int ways)
>> +{
>> +	struct cxl_region *cxlr;
>> +
>> +	mutex_lock(&cxlrd->range_lock);
>> +	cxlr = __construct_new_region(cxlrd, cxled, ways);
>> +	mutex_unlock(&cxlrd->range_lock);
>> +	if (IS_ERR(cxlr))
>> +		return cxlr;
>> +
>> +	if (device_attach(&cxlr->dev) <= 0) {
>> +		dev_err(&cxlr->dev, "failed to create region\n");
>> +		drop_region(cxlr);
>> +		return ERR_PTR(-ENODEV);
>> +	}
>> +
>> +	return cxlr;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_create_region, "CXL");
>> +
>>   static struct cxl_region *
>>   cxl_find_region_by_range(struct cxl_root_decoder *cxlrd, struct range *hpa)
>>   {
>> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
>> index 4802371db00e..50acbd13bcf8 100644
>> --- a/include/cxl/cxl.h
>> +++ b/include/cxl/cxl.h
>> @@ -281,4 +281,7 @@ struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
>>   					     enum cxl_partition_mode mode,
>>   					     resource_size_t alloc);
>>   int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
>> +struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>> +				     struct cxl_endpoint_decoder **cxled,
>> +				     int ways);
>>   #endif /* __CXL_CXL_H__ */