linux-kernel - Re: [PATCH v5 7/7] dax/hmem: Reintroduce Soft Reserved ranges back into the iomem tree

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Message-ID: <81ff49ae-c513-4897-b243-8827ff4ac561@amd.com>
Date: Wed, 28 Jan 2026 14:07:42 -0800
From: "Koralahalli Channabasappa, Smita" <skoralah@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>,
 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, Ard Biesheuvel <ardb@...nel.org>,
 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>,
 Yazen Ghannam <yazen.ghannam@....com>, Dave Jiang <dave.jiang@...el.com>,
 Davidlohr Bueso <dave@...olabs.net>, 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 Kroah-Hartman <gregkh@...uxfoundation.org>,
 Nathan Fontenot <nathan.fontenot@....com>,
 Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
 Benjamin Cheatham <benjamin.cheatham@....com>,
 Zhijian Li <lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>,
 Tomasz Wolski <tomasz.wolski@...itsu.com>
Subject: Re: [PATCH v5 7/7] dax/hmem: Reintroduce Soft Reserved ranges back
 into the iomem tree

On 1/22/2026 8:39 AM, Jonathan Cameron wrote:
> On Thu, 22 Jan 2026 04:55:43 +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 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>
>> Co-developed-by: Zhijian Li <lizhijian@...itsu.com>
>> Signed-off-by: Zhijian Li <lizhijian@...itsu.com>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
>> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
>> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
>> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> A few minor things from a fresh read.
>> ---
>>   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 bcb57d8678d7..f3ef4faf158f 100644
>> --- a/drivers/dax/hmem/hmem.c
>> +++ b/drivers/dax/hmem/hmem.c
>> @@ -64,6 +64,34 @@ struct dax_defer_work {
>>   	struct work_struct 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)
>> +{
>> +	struct resource *soft __free(kfree) =
>> +		kzalloc(sizeof(*soft), GFP_KERNEL);
> 
> On one line. I think it's exactly 80 chars.
> 
>> +	int rc;
>> +
> The declaration and check should be together. For __free stuff inline declarations
> are preferred.
> 
> You fully assign it so kmalloc is all that's needed.
> 	
> 	
> 	struct resource *soft __free(kfree) = kzalloc(sizeof(*soft), GFP_KERNEL);
> 	if (!soft)
> 
> If not, just switch the two declarations.

Sure, I will make the changes.

Thanks
Smita
> 
>> +	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) {
>