Re: [PATCH v7 7/7] dax/hmem: Reintroduce Soft Reserved ranges back into the iomem tree

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Thu, 19 Mar 2026 01:15:00 +0000
Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com> wrote:

> Reworked from a patch by Alison Schofield <alison.schofield@intel.com>
> 
> Reintroduce Soft Reserved range into the iomem_resource tree for HMEM
> to consume.
> 
> This restores visibility in /proc/iomem for ranges actively in use, while
> avoiding the early-boot conflicts that occurred when Soft Reserved was
> published into iomem before CXL window and region discovery.
> 
> Link: https://lore.kernel.org/linux-cxl/29312c0765224ae76862d59a17748c8188fb95f1.1692638817.git.alison.schofield@intel.com/
> Co-developed-by: Alison Schofield <alison.schofield@intel.com>
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> Co-developed-by: Zhijian Li <lizhijian@fujitsu.com>
> Signed-off-by: Zhijian Li <lizhijian@fujitsu.com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
One minor update needed as kmalloc_obj() has shown up in meantime.

Thanks

Jonathan
> ---
>  drivers/dax/hmem/hmem.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
> index 8c574123bd3b..15e462589b92 100644
> --- a/drivers/dax/hmem/hmem.c
> +++ b/drivers/dax/hmem/hmem.c
> @@ -72,6 +72,34 @@ void dax_hmem_flush_work(void)
>  }
>  EXPORT_SYMBOL_GPL(dax_hmem_flush_work);
>  
> +static void remove_soft_reserved(void *r)
> +{
> +	remove_resource(r);
> +	kfree(r);
> +}
> +
> +static int add_soft_reserve_into_iomem(struct device *host,
> +				       const struct resource *res)
> +{
> +	int rc;
> +
> +	struct resource *soft __free(kfree) =
> +		kmalloc(sizeof(*res), GFP_KERNEL);

Update to

	struct resource *soft __free(kfree) = kmalloc_obj(*soft);

Got added in 7.0 with lots of call sites updated via scripting.

Not sure why this had sizeof(*res) rather than sizeof(*soft).
Same type but should have been soft!  If nothing else that would
probably have broken the scripts looking for where we should
be using kmalloc_obj().


	
> +	if (!soft)
> +		return -ENOMEM;
> +
> +	*soft = DEFINE_RES_NAMED_DESC(res->start, (res->end - res->start + 1),
> +				      "Soft Reserved", IORESOURCE_MEM,
> +				      IORES_DESC_SOFT_RESERVED);
> +
> +	rc = insert_resource(&iomem_resource, soft);
> +	if (rc)
> +		return rc;
> +
> +	return devm_add_action_or_reset(host, remove_soft_reserved,
> +					no_free_ptr(soft));
> +}
> +
>  static int hmem_register_device(struct device *host, int target_nid,
>  				const struct resource *res)
>  {
> @@ -94,7 +122,9 @@ static int hmem_register_device(struct device *host, int target_nid,
>  	if (rc != REGION_INTERSECTS)
>  		return 0;
>  
> -	/* TODO: Add Soft-Reserved memory back to iomem */
> +	rc = add_soft_reserve_into_iomem(host, res);
> +	if (rc)
> +		return rc;
>  
>  	id = memregion_alloc(GFP_KERNEL);
>  	if (id < 0) {