Re: [PATCH v4 1/9] dax/hmem, e820, resource: Defer Soft Reserved insertion until hmem is ready

dan.j.williams
2025-12-02T22:19:43Z

Smita Koralahalli wrote:
> From: Dan Williams <dan.j.williams@intel.com>
>
> Insert Soft Reserved memory into a dedicated soft_reserve_resource tree
> instead of the iomem_resource tree at boot. Delay publishing these ranges
> into the iomem hierarchy until ownership is resolved and the HMEM path
> is ready to consume them.
>
> Publishing Soft Reserved ranges into iomem too early conflicts with CXL
> hotplug and prevents region assembly when those ranges overlap CXL
> windows.
>
> Follow up patches will reinsert Soft Reserved ranges into iomem after CXL
> window publication is complete and HMEM is ready to claim the memory. This
> provides a cleaner handoff between EFI-defined memory ranges and CXL
> resource management without trimming or deleting resources later.

Please, when you modify a patch from an original, add your
Co-developed-by: and clarify what you changed.

>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
> ---
> arch/x86/kernel/e820.c | 2 +-
> drivers/cxl/acpi.c | 2 +-
> drivers/dax/hmem/device.c | 4 +-
> drivers/dax/hmem/hmem.c | 7 ++-
> include/linux/ioport.h | 13 +++++-
> kernel/resource.c | 92 +++++++++++++++++++++++++++++++++------
> 6 files changed, 100 insertions(+), 20 deletions(-)
>
[..]
> @@ -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);

It looks like one of the things you changed from my RFC was the addition
of walk_soft_reserve_res_desc() and region_intersects_soft_reserve().
With those APIs not only does this symbol not need to be exported, but
it also can be static / private to resource.c.

> +
> +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 +685,22 @@ int region_intersects(resource_size_t start, size_t size, unsigned long flags,
> }
> EXPORT_SYMBOL_GPL(region_intersects);
>
> +#ifdef CONFIG_EFI_SOFT_RESERVE
> +int region_intersects_soft_reserve(resource_size_t start, size_t size,
> + unsigned long flags, unsigned long desc)
> +{
> + int ret;
> +
> + read_lock(&resource_lock);
> + ret = __region_intersects(&soft_reserve_resource, start, size, flags,
> + desc);
> + read_unlock(&resource_lock);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(region_intersects_soft_reserve);
> +#endif
> +
> void __weak arch_remove_reservations(struct resource *avail)
> {
> }
> @@ -966,7 +1019,7 @@ EXPORT_SYMBOL_GPL(insert_resource);
> * Insert a resource into the resource tree, possibly expanding it in order
> * to make it encompass any conflicting resources.
> */
> -void insert_resource_expand_to_fit(struct resource *root, struct resource *new)
> +void __insert_resource_expand_to_fit(struct resource *root, struct resource *new)
> {
> if (new->parent)
> return;
> @@ -997,7 +1050,20 @@ void insert_resource_expand_to_fit(struct resource *root, struct resource *new)
> * to use this interface. The former are built-in and only the latter,
> * CXL, is a module.
> */
> -EXPORT_SYMBOL_NS_GPL(insert_resource_expand_to_fit, "CXL");
> +EXPORT_SYMBOL_NS_GPL(__insert_resource_expand_to_fit, "CXL");
> +
> +void insert_resource_expand_to_fit(struct resource *new)
> +{
> + struct resource *root = &iomem_resource;
> +
> +#ifdef CONFIG_EFI_SOFT_RESERVE
> + if (new->desc == IORES_DESC_SOFT_RESERVED)
> + root = &soft_reserve_resource;
> +#endif

I can not say I am entirely happy with this change, I would prefer to
avoid ifdef in C, and I would prefer not to break the legacy semantics
of this function, but it meets the spirit of the original RFC without
introducing a new insert_resource_late(). I assume review feedback
requested this?

> + __insert_resource_expand_to_fit(root, new);
> +}
> +EXPORT_SYMBOL_GPL(insert_resource_expand_to_fit);

There are no consumers for this export, so it can be dropped.