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: <697a808e8f420_30951005e@dwillia2-mobl4.notmuch>
Date: Wed, 28 Jan 2026 13:33:02 -0800
From: <dan.j.williams@...el.com>
To: "Koralahalli Channabasappa, Smita" <skoralah@....com>,
	<dan.j.williams@...el.com>, 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>, 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>, Tomasz Wolski
	<tomasz.wolski@...itsu.com>
Subject: Re: [PATCH v5 4/7] cxl/region: Add helper to check Soft Reserved
 containment by CXL regions

Koralahalli Channabasappa, Smita wrote:
[..]
> > 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.
> 
> Hmm, My reading of your earlier guidance was that this logic is meant to 
> be coarse, and is acceptable to fall back to HMEM if firmware 
> descriptions don’t line up cleanly.
> 
> If firmware takes liberties and publishes ranges that don’t neatly 
> contain inside a committed region resource, my assumption was that 
> failing the containment check and falling back is acceptable.
> 
> However, given that the SR ranges HMEM walks are already filtered by 
> ACPI HMAT, and that there is a relatively low likelihood that a single 
> HMAT range spans multiple committed CXL regions, it would be sufficient 
> to treat any overlap with a committed region as acceptable?

Oh, am I reading the polarity wrong...? /me reads patch 6.

Yes, I was missing that cxl_contains_soft_reserve() is doing an
"overlap" check and then cxl_region_contains_soft_reserve() is making
sure it lines up exactly.

So yes, the way you have it matches what I expected and I was confused
reading patch 4 in isolation.

I think cxl_contains_soft_reserve() might want to be named differently
since it is validating that any overlap is precisely contained. Perhaps
soft_reserve_has_cxl_match()?