Re: [PATCH 5/6] dax/hmem: Reintroduce Soft Reserved ranges back into the iomem tree

[Dave Jiang <dave.jiang@xxxxxxxxx>]

On 8/21/25 8:42 PM, Smita Koralahalli wrote:
> Reworked from a patch by Alison Schofield <alison.schofield@xxxxxxxxx>
> 
> Reintroduce Soft Reserved range into the iomem_resource tree for dax_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@xxxxxxxxx/
> Co-developed-by: Alison Schofield <alison.schofield@xxxxxxxxx>
> Signed-off-by: Alison Schofield <alison.schofield@xxxxxxxxx>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>

Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> ---
>  drivers/dax/hmem/hmem.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
> index 90978518e5f4..24a6e7e3d916 100644
> --- a/drivers/dax/hmem/hmem.c
> +++ b/drivers/dax/hmem/hmem.c
> @@ -93,6 +93,40 @@ static void process_defer_work(struct work_struct *_work)
>  	walk_hmem_resources(&pdev->dev, handle_deferred_cxl);
>  }
>  
> +static void remove_soft_reserved(void *data)
> +{
> +	struct resource *r = data;
> +
> +	remove_resource(r);
> +	kfree(r);
> +}
> +
> +static int add_soft_reserve_into_iomem(struct device *host,
> +				       const struct resource *res)
> +{
> +	struct resource *soft = kzalloc(sizeof(*soft), GFP_KERNEL);
> +	int rc;
> +
> +	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) {
> +		kfree(soft);
> +		return rc;
> +	}
> +
> +	rc = devm_add_action_or_reset(host, remove_soft_reserved, soft);
> +	if (rc)
> +		return rc;
> +
> +	return 0;
> +}
> +
>  static int hmem_register_device(struct device *host, int target_nid,
>  				const struct resource *res)
>  {
> @@ -125,6 +159,10 @@ static int hmem_register_device(struct device *host, int target_nid,
>  					    IORES_DESC_SOFT_RESERVED);
>  	if (rc != REGION_INTERSECTS)
>  		return 0;
> +
> +	rc = add_soft_reserve_into_iomem(host, res);
> +	if (rc)
> +		return rc;
>  #else
>  	rc = region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
>  			       IORES_DESC_SOFT_RESERVED);