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 <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
---
   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


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