linux-kernel - Re: [RFC] CXL/ACPI: Remove overlapping Soft Reserved regions before adding CFMW resources

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Message-ID: <aQznzIP6h5NibJM6@gourry-fedora-PF4VCD3F>
Date: Thu, 6 Nov 2025 13:24:12 -0500
From: Gregory Price <gourry@...rry.net>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc: Nathan Fontenot <nathan.fontenot@....com>,
	"Koralahalli Channabasappa, Smita" <Smita.KoralahalliChannabasappa@....com>,
	"Bowman, Terry" <terry.bowman@....com>,
	Alison Schofield <alison.schofield@...el.com>,
	"linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"dave.jiang@...el.com" <dave.jiang@...el.com>,
	"vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
	Robert Richter <rrichter@....com>, Fan Ni <fan.ni@...sung.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	"Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] CXL/ACPI: Remove overlapping Soft Reserved regions before
 adding CFMW resources

On Fri, Jul 11, 2025 at 05:34:27AM +0000, Zhijian Li (Fujitsu) wrote:
> 
> 
> On 11/07/2025 05:15, Nathan Fontenot wrote:
> In this case(with your V4 patch), we would see:
> ```
> 5d0000000-6cfffffff : CXL Window 0
>    5d0000000-6cfffffff : region0
> ```
> Actually, it cannot be consumed by the hmem/dax_hmem neither.
> 
> This made me realize that my current idea ignores the case of CXL_ACPI=y && CXL_REGION=n. I quickly tested it(I will take a deeper look later):
> 
> After the OS boots, we can see this resource. Can anyone tell me how to create the corresponding dax_region? Because I tried using dax create-device without success.
> ```
> 5d0000000-6cfffffff : CXL Window 0
>    5d0000000-6cfffffff : Soft Reserved
> ```
> 

with CXL_REGION=n you cannot create the dax region.

region0 --creates-> dax_region0 --creates-> dax0

all you've done here by setting CXL_REGION=N is break the probe chain
but otherwise successfully attributed the memory to the CXL driver.

~Gregory