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

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Message-ID: <20250910144136.000002e2@huawei.com>
Date: Wed, 10 Sep 2025 14:41:36 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, Davidlohr Bueso <dave@...olabs.net>, Dave Jiang
	<dave.jiang@...el.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
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	<ming.li@...omail.com>, Jeff Johnson <jeff.johnson@....qualcomm.com>, Ying
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	"Peter Zijlstra" <peterz@...radead.org>, Greg KH
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	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 Fri, 22 Aug 2025 03:42:01 +0000
Smita Koralahalli <Smita.KoralahalliChannabasappa@....com> 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>
A few trivial things inline. Not are important enough to need a change though.

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.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);

Type doesn't really help us here so why not skip the local variable.
	remove_resource(data);
	kfree(data);

Though I'd rename data to 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);

Could use __free() magic here and steal the pointer when you setup the
devm action below.  Only a small simplification in this case, so up to
you.

> +		return rc;
> +	}
> +
> +	rc = devm_add_action_or_reset(host, remove_soft_reserved, soft);
> +	if (rc)
> +		return rc;
> +
> +	return 0;

Trivial:

	return dev_add_action_or_reset(host...)

> +}