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

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Message-ID: <14d94e89-8342-4bd7-9c53-a3b46e22caa7@intel.com>
Date: Thu, 4 Sep 2025 11:14:15 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 linux-pm@...r.kernel.org
Cc: Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Dan Williams <dan.j.williams@...el.com>, Matthew Wilcox
 <willy@...radead.org>, Jan Kara <jack@...e.cz>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <len.brown@...el.com>,
 Pavel Machek <pavel@...nel.org>, Li Ming <ming.li@...omail.com>,
 Jeff Johnson <jeff.johnson@....qualcomm.com>,
 Ying Huang <huang.ying.caritas@...il.com>,
 Yao Xingtao <yaoxt.fnst@...itsu.com>, Peter Zijlstra <peterz@...radead.org>,
 Greg KH <gregkh@...uxfoundation.org>,
 Nathan Fontenot <nathan.fontenot@....com>,
 Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
 Benjamin Cheatham <benjamin.cheatham@....com>,
 PradeepVineshReddy Kodamati <PradeepVineshReddy.Kodamati@....com>,
 Zhijian Li <lizhijian@...itsu.com>
Subject: Re: [PATCH 5/6] dax/hmem: Reintroduce Soft Reserved ranges back into
 the iomem tree

On 8/21/25 8:42 PM, Smita Koralahalli wrote:
> Reworked from a patch by Alison Schofield <alison.schofield@...el.com>
> 
> 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@intel.com/
> Co-developed-by: Alison Schofield <alison.schofield@...el.com>
> Signed-off-by: Alison Schofield <alison.schofield@...el.com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> ---
>  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);