Re: [PATCH v2 3/4] dax: Update hmem resource/device registration

["Fontenot, Nathan" <nafonten@amd.com>]

On 1/21/2025 5:14 PM, Ira Weiny wrote:
> Fontenot, Nathan wrote:
>> On 1/16/2025 4:28 PM, Ira Weiny wrote:
>>> Nathan Fontenot wrote:
>>>> In order to handle registering hmem devices for SOFT RESERVE reources
>>>                                                               ^^^^^^^^^
>>>                                                               resources
>>>
>>>> that are added late in boot update the hmem_register_resource(),
>>>> hmem_register_device(), and walk_hmem_resources() interfaces.
>>>>
>>>> Remove the target_nid arg to hmem_register_resource(). The target nid
>>>> value is calculated from the resource start address and not used until
>>>> registering a device for the resource. Move the target nid calculation
>>>> to hmem_register_device().
>>>>
>>>> To allow for registering hmem devices outside of the hmem dax driver
>>>> probe routine save the dax hmem platform driver during probe. The
>>>> hmem_register_device() interface can then drop the host and target
>>>> nid parameters.
>>>>
>>>> There should be no functional changes.
>>>>
>>>> Signed-off-by: Nathan Fontenot <nathan.fontenot@amd.com>
>>>> ---
>>>>  drivers/acpi/numa/hmat.c  |  7 ++-----
>>>>  drivers/dax/hmem/device.c | 14 ++++++--------
>>>>  drivers/dax/hmem/hmem.c   | 12 ++++++++----
>>>>  include/linux/dax.h       |  9 ++++-----
>>>>  4 files changed, 20 insertions(+), 22 deletions(-)
>>>>
>>>> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
>>>> index 1a902a02390f..23d4b3ad6d88 100644
>>>> --- a/drivers/acpi/numa/hmat.c
>>>> +++ b/drivers/acpi/numa/hmat.c
>>>> @@ -857,11 +857,8 @@ static void hmat_register_target_devices(struct memory_target *target)
>>>>  	if (!IS_ENABLED(CONFIG_DEV_DAX_HMEM))
>>>>  		return;
>>>>  
>>>> -	for (res = target->memregions.child; res; res = res->sibling) {
>>>> -		int target_nid = pxm_to_node(target->memory_pxm);
>>>> -
>>>> -		hmem_register_resource(target_nid, res);
>>>> -	}
>>>> +	for (res = target->memregions.child; res; res = res->sibling)
>>>> +		hmem_register_resource(res);
>>>>  }
>>>>  
>>>>  static void hmat_register_target(struct memory_target *target)
>>>> diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
>>>> index f9e1a76a04a9..ae25e08a636f 100644
>>>> --- a/drivers/dax/hmem/device.c
>>>> +++ b/drivers/dax/hmem/device.c
>>>> @@ -17,14 +17,14 @@ static struct resource hmem_active = {
>>>>  	.flags = IORESOURCE_MEM,
>>>>  };
>>>>  
>>>> -int walk_hmem_resources(struct device *host, walk_hmem_fn fn)
>>>> +int walk_hmem_resources(walk_hmem_fn fn)
>>>>  {
>>>>  	struct resource *res;
>>>>  	int rc = 0;
>>>>  
>>>>  	mutex_lock(&hmem_resource_lock);
>>>>  	for (res = hmem_active.child; res; res = res->sibling) {
>>>> -		rc = fn(host, (int) res->desc, res);
>>>> +		rc = fn(res);
>>>>  		if (rc)
>>>>  			break;
>>>>  	}
>>>> @@ -33,7 +33,7 @@ int walk_hmem_resources(struct device *host, walk_hmem_fn fn)
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(walk_hmem_resources);
>>>>  
>>>> -static void __hmem_register_resource(int target_nid, struct resource *res)
>>>> +static void __hmem_register_resource(struct resource *res)
>>>>  {
>>>>  	struct platform_device *pdev;
>>>>  	struct resource *new;
>>>> @@ -46,8 +46,6 @@ static void __hmem_register_resource(int target_nid, struct resource *res)
>>>>  		return;
>>>>  	}
>>>>  
>>>> -	new->desc = target_nid;
>>>> -
>>>>  	if (platform_initialized)
>>>>  		return;
>>>>  
>>>> @@ -64,19 +62,19 @@ static void __hmem_register_resource(int target_nid, struct resource *res)
>>>>  		platform_initialized = true;
>>>>  }
>>>>  
>>>> -void hmem_register_resource(int target_nid, struct resource *res)
>>>> +void hmem_register_resource(struct resource *res)
>>>>  {
>>>>  	if (nohmem)
>>>>  		return;
>>>>  
>>>>  	mutex_lock(&hmem_resource_lock);
>>>> -	__hmem_register_resource(target_nid, res);
>>>> +	__hmem_register_resource(res);
>>>>  	mutex_unlock(&hmem_resource_lock);
>>>>  }
>>>>  
>>>>  static __init int hmem_register_one(struct resource *res, void *data)
>>>>  {
>>>> -	hmem_register_resource(phys_to_target_node(res->start), res);
>>>> +	hmem_register_resource(res);
>>>>  
>>>>  	return 0;
>>>>  }
>>>> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
>>>> index 5e7c53f18491..088f4060d4d5 100644
>>>> --- a/drivers/dax/hmem/hmem.c
>>>> +++ b/drivers/dax/hmem/hmem.c
>>>> @@ -9,6 +9,8 @@
>>>>  static bool region_idle;
>>>>  module_param_named(region_idle, region_idle, bool, 0644);
>>>>  
>>>> +static struct platform_device *dax_hmem_pdev;
>>>
>>> I don't think you can assume there is only ever 1 hmem platform device.
>>>
>>> hmat_register_target_devices() in particular iterates multiple memory
>>> regions and will create more than one.
>>>
>>> What am I missing?
>>
>> You may be correct that there can be more than one hmem platform device.
>> I was making this change based on a comment from Dan that it may not matter
>> which platform device these are created against.
> 
> If that is true I think there should be a big comment around this code
> explaining why it is ok to have the platform device being allocated in
> this call unregistered when a different platform device (host) is
> released.
> 
> IOW hmem_register_device() calls two devm_*() functions using host as the
> device used to trigger an action.  It is not entirely clear to me why that
> change is safe here.
> 
>>
>> I could be wrong in that assumption. If so we'll need to figure lout how to
>> determine which platform device a soft reserve resource would be created
>> against when they are added later in boot from a notification by the
>> srmem notification chain.
> 
> I see that it would be more difficult to track.  And I'm ok if it really
> does work.  But just looking at the commit message and code I don't see
> how this does not at least introduce a functional change.

I'm going to go back and take a look at this again. I went this direction
using the approach of having the srmem notification chain. The dax driver
then adds soft reserves outside of a probe routine and don't have a
platform device associated with them.

-Nathan

> 
> Ira
> 
>>
>> -Nathan
>>
>>> Ira
>>>
>>>> +
>>>>  static int dax_hmem_probe(struct platform_device *pdev)
>>>>  {
>>>>  	unsigned long flags = IORESOURCE_DAX_KMEM;
>>>> @@ -59,13 +61,13 @@ static void release_hmem(void *pdev)
>>>>  	platform_device_unregister(pdev);
>>>>  }
>>>>  
>>>> -static int hmem_register_device(struct device *host, int target_nid,
>>>> -				const struct resource *res)
>>>> +static int hmem_register_device(const struct resource *res)
>>>>  {
>>>> +	struct device *host = &dax_hmem_pdev->dev;
>>>>  	struct platform_device *pdev;
>>>>  	struct memregion_info info;
>>>> +	int target_nid, rc;
>>>>  	long id;
>>>> -	int rc;
>>>>  
>>>>  	if (IS_ENABLED(CONFIG_CXL_REGION) &&
>>>>  	    region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
>>>> @@ -94,6 +96,7 @@ static int hmem_register_device(struct device *host, int target_nid,
>>>>  		return -ENOMEM;
>>>>  	}
>>>>  
>>>> +	target_nid = phys_to_target_node(res->start);
>>>>  	pdev->dev.numa_node = numa_map_to_online_node(target_nid);
>>>>  	info = (struct memregion_info) {
>>>>  		.target_node = target_nid,
>>>> @@ -125,7 +128,8 @@ static int hmem_register_device(struct device *host, int target_nid,
>>>>  
>>>>  static int dax_hmem_platform_probe(struct platform_device *pdev)
>>>>  {
>>>> -	return walk_hmem_resources(&pdev->dev, hmem_register_device);
>>>> +	dax_hmem_pdev = pdev;
>>>> +	return walk_hmem_resources(hmem_register_device);
>>>>  }
>>>>  
>>>>  static struct platform_driver dax_hmem_platform_driver = {
>>>> diff --git a/include/linux/dax.h b/include/linux/dax.h
>>>> index 9d3e3327af4c..beaa4bcb515c 100644
>>>> --- a/include/linux/dax.h
>>>> +++ b/include/linux/dax.h
>>>> @@ -276,14 +276,13 @@ static inline int dax_mem2blk_err(int err)
>>>>  }
>>>>  
>>>>  #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
>>>> -void hmem_register_resource(int target_nid, struct resource *r);
>>>> +void hmem_register_resource(struct resource *r);
>>>>  #else
>>>> -static inline void hmem_register_resource(int target_nid, struct resource *r)
>>>> +static inline void hmem_register_resource(struct resource *r)
>>>>  {
>>>>  }
>>>>  #endif
>>>>  
>>>> -typedef int (*walk_hmem_fn)(struct device *dev, int target_nid,
>>>> -			    const struct resource *res);
>>>> -int walk_hmem_resources(struct device *dev, walk_hmem_fn fn);
>>>> +typedef int (*walk_hmem_fn)(const struct resource *res);
>>>> +int walk_hmem_resources(walk_hmem_fn fn);
>>>>  #endif
>>>> -- 
>>>> 2.43.0
>>>>
>>>>
>>>
>>>
>>
> 
>