linux-kernel - Re: [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL and dax

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Message-ID: <876c01d5-0b32-4be0-92c7-acfdbf96767b@amd.com>
Date: Mon, 29 Sep 2025 21:04:42 -0700
From: "Koralahalli Channabasappa, Smita" <skoralah@....com>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>,
 Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
 "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
 "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
 "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Cc: Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 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 <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>,
 "Xingtao Yao (Fujitsu)" <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>
Subject: Re: [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL
 and dax_hmem

On 8/31/2025 8:28 PM, Zhijian Li (Fujitsu) wrote:
> 
> 
> On 22/08/2025 11:41, Smita Koralahalli wrote:
>> Update Kconfig and runtime checks to better coordinate dax_cxl and dax_hmem
>> registration.
>>
>> Add explicit Kconfig ordering so that CXL_ACPI and CXL_PCI must be
>> initialized before DEV_DAX_HMEM.
> 
> Is this dependency statement fully accurate? To clarify, another prerequisite for
> this ordering to work correctly is that dax_hmem must explicitly call
> `request_module("cxl_acpi")` and `request_module("cxl_pci")` during its initialization.
>    
> Therefore, I recommend consolidating the following patches into a single commit
> to ensure atomic handling of the initialization order:
> - [PATCH 2/6] dax/hmem: Request cxl_acpi and cxl_pci before walking Soft Reserved ranges
> - [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL and dax_hmem
> 
> Thanks
> Zhijian

I have merged 2/6 and 3/6 in v2.

Thanks
Smita

>> This prevents dax_hmem from consuming
>> Soft Reserved ranges before CXL drivers have had a chance to claim them.
>>
>> Replace IS_ENABLED(CONFIG_CXL_REGION) with IS_ENABLED(CONFIG_DEV_DAX_CXL)
>> so the code more precisely reflects when CXL-specific DAX coordination is
>> expected.
>>
>> This ensures that ownership of Soft Reserved ranges is consistently
>> handed off to the CXL stack when DEV_DAX_CXL is configured.