linux-kernel - Re: [PATCH v5 4/7] cxl/region: Add helper to check Soft Reserved containment by CXL regions

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Message-ID: <697935261679_1d33100de@dwillia2-mobl4.notmuch>
Date: Tue, 27 Jan 2026 13:59:02 -0800
From: <dan.j.williams@...el.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>
CC: 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>,
	Jonathan Cameron <jonathan.cameron@...wei.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>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Tomasz Wolski
	<tomasz.wolski@...itsu.com>
Subject: Re: [PATCH v5 4/7] cxl/region: Add helper to check Soft Reserved
 containment by CXL regions

Smita Koralahalli wrote:
> Add a helper to determine whether a given Soft Reserved memory range is
> fully contained within the committed CXL region.
> 
> This helper provides a primitive for policy decisions in subsequent
> patches such as co-ordination with dax_hmem to determine whether CXL has
> fully claimed ownership of Soft Reserved memory ranges.
> 
> No functional changes are introduced by this patch.
> 
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> ---
>  drivers/cxl/core/region.c | 29 +++++++++++++++++++++++++++++
>  drivers/cxl/cxl.h         |  5 +++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 45ee598daf95..9827a6dd3187 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3875,6 +3875,35 @@ static int cxl_region_debugfs_poison_clear(void *data, u64 offset)
>  DEFINE_DEBUGFS_ATTRIBUTE(cxl_poison_clear_fops, NULL,
>  			 cxl_region_debugfs_poison_clear, "%llx\n");
>  
> +static int cxl_region_contains_sr_cb(struct device *dev, void *data)
> +{
> +	struct resource *res = data;
> +	struct cxl_region *cxlr;
> +	struct cxl_region_params *p;
> +
> +	if (!is_cxl_region(dev))
> +		return 0;
> +
> +	cxlr = to_cxl_region(dev);
> +	p = &cxlr->params;
> +
> +	if (p->state != CXL_CONFIG_COMMIT)
> +		return 0;
> +
> +	if (!p->res)
> +		return 0;
> +
> +	return resource_contains(p->res, res) ? 1 : 0;

I suspect this is too precise and this should instead be
resource_overlaps(). Because, in the case where the platform is taking
liberties with the specification, there is a high likelihood that
driver's view of the region does not neatly contain the range published
in the memory map.

There is also the problem with the fact that firmware does not
necessarily need to split memory map entries on region boundaries. That
gets slightly better if this @res argument is the range boundary that
has been adjusted by HMAT, but still not a guarantee per the spec.

> +}
> +
> +bool cxl_region_contains_soft_reserve(const struct resource *res)
> +{
> +	guard(rwsem_read)(&cxl_rwsem.region);
> +	return bus_for_each_dev(&cxl_bus_type, NULL, (void *)res,

No, need to cast pointers to 'void *'.