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

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

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.



> +	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").


>   	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.


Thanks
Zhijian