Re: [PATCH 1/6] dax/hmem, e820, resource: Defer Soft Reserved registration until hmem is ready

["Koralahalli Channabasappa, Smita" <skoralah@amd.com>]

Hi Zhijian,

Sorry for the delay here.

On 8/31/2025 7:59 PM, Zhijian Li (Fujitsu) wrote:
> 
> 
> On 22/08/2025 11:41, Smita Koralahalli wrote:
>> Insert Soft Reserved memory into a dedicated soft_reserve_resource tree
>> instead of the iomem_resource tree at boot.
>>
>> Publishing Soft Reserved ranges into iomem too early causes conflicts with
>> CXL hotplug and region assembly failure, especially when Soft Reserved
>> overlaps CXL regions.
>>
>> Re-inserting these ranges into iomem will be handled in follow-up patches,
>> after ensuring CXL window publication ordering is stabilized and when the
>> dax_hmem is ready to consume them.
>>
>> This avoids trimming or deleting resources later and provides a cleaner
>> handoff between EFI-defined memory and CXL resource management.
>>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
>> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>> ---
>>    arch/x86/kernel/e820.c    |  2 +-
>>    drivers/dax/hmem/device.c |  4 +--
>>    drivers/dax/hmem/hmem.c   |  8 +++++
>>    include/linux/ioport.h    | 24 +++++++++++++
>>    kernel/resource.c         | 73 +++++++++++++++++++++++++++++++++------
>>    5 files changed, 97 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
>> index c3acbd26408b..aef1ff2cabda 100644
>> --- a/arch/x86/kernel/e820.c
>> +++ b/arch/x86/kernel/e820.c
>> @@ -1153,7 +1153,7 @@ void __init e820__reserve_resources_late(void)
>>    	res = e820_res;
>>    	for (i = 0; i < e820_table->nr_entries; i++) {
>>    		if (!res->parent && res->end)
>> -			insert_resource_expand_to_fit(&iomem_resource, res);
>> +			insert_resource_late(res);
>>    		res++;
>>    	}
>>    
>> diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
>> index f9e1a76a04a9..22732b729017 100644
>> --- a/drivers/dax/hmem/device.c
>> +++ b/drivers/dax/hmem/device.c
>> @@ -83,8 +83,8 @@ static __init int hmem_register_one(struct resource *res, void *data)
>>    
>>    static __init int hmem_init(void)
>>    {
>> -	walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED,
>> -			IORESOURCE_MEM, 0, -1, NULL, hmem_register_one);
>> +	walk_soft_reserve_res_desc(IORES_DESC_SOFT_RESERVED, IORESOURCE_MEM, 0,
>> +				   -1, NULL, hmem_register_one);
>>    	return 0;
>>    }
>>    
>> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
>> index c18451a37e4f..d5b8f06d531e 100644
>> --- a/drivers/dax/hmem/hmem.c
>> +++ b/drivers/dax/hmem/hmem.c
>> @@ -73,10 +73,18 @@ static int hmem_register_device(struct device *host, int target_nid,
>>    		return 0;
>>    	}
>>    
>> +#ifdef CONFIG_EFI_SOFT_RESERVE
> 
> 
> Note that dax_kmem currently depends on CONFIG_EFI_SOFT_RESERVED, so this conditional check may be redundant.

Removed in v2.

> 
> 
> 
>> +	rc = region_intersects_soft_reserve(res->start, resource_size(res),
>> +					    IORESOURCE_MEM,
>> +					    IORES_DESC_SOFT_RESERVED);
>> +	if (rc != REGION_INTERSECTS)
>> +		return 0;
>> +#else
>>    	rc = region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
>>    			       IORES_DESC_SOFT_RESERVED);
>>    	if (rc != REGION_INTERSECTS)
>>    		return 0;
>> +#endif
>>    
> 
> Additionally, please add a TODO note here (e.g., "Add soft-reserved memory back to iomem").

Added.

> 
> 
>>    	id = memregion_alloc(GFP_KERNEL);
>>    	if (id < 0) {
>> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>> index e8b2d6aa4013..889bc4982777 100644
>> --- a/include/linux/ioport.h
>> +++ b/include/linux/ioport.h
>> @@ -232,6 +232,9 @@ struct resource_constraint {
>>    /* PC/ISA/whatever - the normal PC address spaces: IO and memory */
>>    extern struct resource ioport_resource;
>>    extern struct resource iomem_resource;
>> +#ifdef CONFIG_EFI_SOFT_RESERVE
>> +extern struct resource soft_reserve_resource;
>> +#endif
>>    
>>    extern struct resource *request_resource_conflict(struct resource *root, struct resource *new);
>>    extern int request_resource(struct resource *root, struct resource *new);
>> @@ -255,6 +258,22 @@ int adjust_resource(struct resource *res, resource_size_t start,
>>    		    resource_size_t size);
>>    resource_size_t resource_alignment(struct resource *res);
>>    
>> +
>> +#ifdef CONFIG_EFI_SOFT_RESERVE
>> +static inline void insert_resource_late(struct resource *new)
>> +{
>> +	if (new->desc == IORES_DESC_SOFT_RESERVED)
>> +		insert_resource_expand_to_fit(&soft_reserve_resource, new);
>> +	else
>> +		insert_resource_expand_to_fit(&iomem_resource, new);
>> +}
>> +#else
>> +static inline void insert_resource_late(struct resource *new)
>> +{
>> +	insert_resource_expand_to_fit(&iomem_resource, new);
>> +}
>> +#endif
>> +
>>    /**
>>     * resource_set_size - Calculate resource end address from size and start
>>     * @res: Resource descriptor
>> @@ -409,6 +428,11 @@ walk_system_ram_res_rev(u64 start, u64 end, void *arg,
>>    extern int
>>    walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start, u64 end,
>>    		    void *arg, int (*func)(struct resource *, void *));
>> +int walk_soft_reserve_res_desc(unsigned long desc, unsigned long flags,
>> +			       u64 start, u64 end, void *arg,
>> +			       int (*func)(struct resource *, void *));
>> +int region_intersects_soft_reserve(resource_size_t start, size_t size,
>> +				   unsigned long flags, unsigned long desc);
>>    
>>    struct resource *devm_request_free_mem_region(struct device *dev,
>>    		struct resource *base, unsigned long size);
>> diff --git a/kernel/resource.c b/kernel/resource.c
>> index f9bb5481501a..8479a99441e2 100644
>> --- a/kernel/resource.c
>> +++ b/kernel/resource.c
>> @@ -321,13 +321,14 @@ static bool is_type_match(struct resource *p, unsigned long flags, unsigned long
>>    }
>>    
>>    /**
>> - * find_next_iomem_res - Finds the lowest iomem resource that covers part of
>> - *			 [@start..@end].
>> + * find_next_res - Finds the lowest resource that covers part of
>> + *		   [@start..@end].
>>     *
>>     * If a resource is found, returns 0 and @*res is overwritten with the part
>>     * of the resource that's within [@start..@end]; if none is found, returns
>>     * -ENODEV.  Returns -EINVAL for invalid parameters.
>>     *
>> + * @parent:	resource tree root to search
>>     * @start:	start address of the resource searched for
>>     * @end:	end address of same resource
>>     * @flags:	flags which the resource must have
>> @@ -337,9 +338,9 @@ static bool is_type_match(struct resource *p, unsigned long flags, unsigned long
>>     * The caller must specify @start, @end, @flags, and @desc
>>     * (which may be IORES_DESC_NONE).
>>     */
>> -static int find_next_iomem_res(resource_size_t start, resource_size_t end,
>> -			       unsigned long flags, unsigned long desc,
>> -			       struct resource *res)
>> +static int find_next_res(struct resource *parent, resource_size_t start,
>> +			 resource_size_t end, unsigned long flags,
>> +			 unsigned long desc, struct resource *res)
>>    {
>>    	struct resource *p;
>>    
>> @@ -351,7 +352,7 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,
>>    
>>    	read_lock(&resource_lock);
>>    
>> -	for_each_resource(&iomem_resource, p, false) {
>> +	for_each_resource(parent, p, false) {
>>    		/* If we passed the resource we are looking for, stop */
>>    		if (p->start > end) {
>>    			p = NULL;
>> @@ -382,16 +383,23 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,
>>    	return p ? 0 : -ENODEV;
>>    }
>>    
>> -static int __walk_iomem_res_desc(resource_size_t start, resource_size_t end,
>> -				 unsigned long flags, unsigned long desc,
>> -				 void *arg,
>> -				 int (*func)(struct resource *, void *))
>> +static int find_next_iomem_res(resource_size_t start, resource_size_t end,
>> +			       unsigned long flags, unsigned long desc,
>> +			       struct resource *res)
>> +{
>> +	return find_next_res(&iomem_resource, start, end, flags, desc, res);
>> +}
>> +
>> +static int walk_res_desc(struct resource *parent, resource_size_t start,
>> +			 resource_size_t end, unsigned long flags,
>> +			 unsigned long desc, void *arg,
>> +			 int (*func)(struct resource *, void *))
>>    {
>>    	struct resource res;
>>    	int ret = -EINVAL;
>>    
>>    	while (start < end &&
>> -	       !find_next_iomem_res(start, end, flags, desc, &res)) {
>> +	       !find_next_res(parent, start, end, flags, desc, &res)) {
>>    		ret = (*func)(&res, arg);
>>    		if (ret)
>>    			break;
>> @@ -402,6 +410,15 @@ static int __walk_iomem_res_desc(resource_size_t start, resource_size_t end,
>>    	return ret;
>>    }
>>    
>> +static int __walk_iomem_res_desc(resource_size_t start, resource_size_t end,
>> +				 unsigned long flags, unsigned long desc,
>> +				 void *arg,
>> +				 int (*func)(struct resource *, void *))
>> +{
>> +	return walk_res_desc(&iomem_resource, start, end, flags, desc, arg, func);
>> +}
>> +
>> +
>>    /**
>>     * walk_iomem_res_desc - Walks through iomem resources and calls func()
>>     *			 with matching resource ranges.
>> @@ -426,6 +443,26 @@ int walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start,
>>    }
>>    EXPORT_SYMBOL_GPL(walk_iomem_res_desc);
>>    
>> +#ifdef CONFIG_EFI_SOFT_RESERVE
>> +struct resource soft_reserve_resource = {
>> +	.name	= "Soft Reserved",
>> +	.start	= 0,
>> +	.end	= -1,
>> +	.desc	= IORES_DESC_SOFT_RESERVED,
>> +	.flags	= IORESOURCE_MEM,
>> +};
>> +EXPORT_SYMBOL_GPL(soft_reserve_resource);
>> +
>> +int walk_soft_reserve_res_desc(unsigned long desc, unsigned long flags,
>> +			       u64 start, u64 end, void *arg,
>> +			       int (*func)(struct resource *, void *))
>> +{
>> +	return walk_res_desc(&soft_reserve_resource, start, end, flags, desc,
>> +			     arg, func);
>> +}
>> +EXPORT_SYMBOL_GPL(walk_soft_reserve_res_desc);
>> +#endif
>> +
>>    /*
>>     * This function calls the @func callback against all memory ranges of type
>>     * System RAM which are marked as IORESOURCE_SYSTEM_RAM and IORESOUCE_BUSY.
>> @@ -648,6 +685,20 @@ int region_intersects(resource_size_t start, size_t size, unsigned long flags,
>>    }
>>    EXPORT_SYMBOL_GPL(region_intersects);
>>    
>> +int region_intersects_soft_reserve(resource_size_t start, size_t size,
>> +				   unsigned long flags, unsigned long desc)
> 
> 
> Shouldn't this function be implemented uder `#if CONFIG_EFI_SOFT_RESERVE`? Otherwise it may cause compilation failures when the config is disabled.

Fixed it.

Thanks
Smita
> 
> Thanks
> Zhijian