linux-kernel - Re: [PATCH 2/6] dax/hmem: Request cxl_acpi and cxl

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Message-ID: <1e4344b9-490e-47a2-902b-3d5e84ca4b67@fujitsu.com>
Date: Mon, 1 Sep 2025 03:08:07 +0000
From: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To: 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 2/6] dax/hmem: Request cxl_acpi and cxl_pci before walking
 Soft Reserved ranges


I personally recommend that this patch be moved to position 1/6 in the series, as it specifically addresses the existing issue.


Thanks
Zhijian


On 22/08/2025 11:41, Smita Koralahalli wrote:
> Ensure that cxl_acpi has published CXL Window resources before dax_hmem
> walks Soft Reserved ranges.
> 
> Replace MODULE_SOFTDEP("pre: cxl_acpi") with an explicit, synchronous
> request_module("cxl_acpi"). MODULE_SOFTDEP() only guarantees eventual
> loading, it does not enforce that the dependency has finished init
> before the current module runs. This can cause dax_hmem to start before
> cxl_acpi has populated the resource tree, breaking detection of overlaps
> between Soft Reserved and CXL Windows.
> 
> Also, request cxl_pci before dax_hmem walks Soft Reserved ranges. Unlike
> cxl_acpi, cxl_pci attach is asynchronous and creates dependent devices
> that trigger further module loads. Asynchronous probe flushing
> (wait_for_device_probe()) is added later in the series in a deferred
> context before dax_hmem makes ownership decisions for Soft Reserved
> ranges.
> 
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>   drivers/dax/hmem/hmem.c | 17 ++++++++++-------
>   1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
> index d5b8f06d531e..9277e5ea0019 100644
> --- a/drivers/dax/hmem/hmem.c
> +++ b/drivers/dax/hmem/hmem.c
> @@ -146,6 +146,16 @@ static __init int dax_hmem_init(void)
>   {
>   	int rc;
>   
> +	/*
> +	 * Ensure that cxl_acpi and cxl_pci have a chance to kick off
> +	 * CXL topology discovery at least once before scanning the
> +	 * iomem resource tree for IORES_DESC_CXL resources.
> +	 */
> +	if (IS_ENABLED(CONFIG_DEV_DAX_CXL)) {
> +		request_module("cxl_acpi");
> +		request_module("cxl_pci");
> +	}
> +
>   	rc = platform_driver_register(&dax_hmem_platform_driver);
>   	if (rc)
>   		return rc;
> @@ -166,13 +176,6 @@ static __exit void dax_hmem_exit(void)
>   module_init(dax_hmem_init);
>   module_exit(dax_hmem_exit);
>   
> -/* Allow for CXL to define its own dax regions */
> -#if IS_ENABLED(CONFIG_CXL_REGION)
> -#if IS_MODULE(CONFIG_CXL_ACPI)
> -MODULE_SOFTDEP("pre: cxl_acpi");
> -#endif
> -#endif
> -
>   MODULE_ALIAS("platform:hmem*");
>   MODULE_ALIAS("platform:hmem_platform*");
>   MODULE_DESCRIPTION("HMEM DAX: direct access to 'specific purpose' memory");