linux-kernel - Re: [PATCH v5 6/7] dax/hmem, cxl: Defer and resolve ownership of Soft Reserved memory ranges

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Message-ID: <69794d438629e_1d33100f3@dwillia2-mobl4.notmuch>
Date: Tue, 27 Jan 2026 15:41:55 -0800
From: <dan.j.williams@...el.com>
To: Alejandro Lucero Palau <alucerop@....com>, <dan.j.williams@...el.com>,
	"Koralahalli Channabasappa, Smita" <skoralah@....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 6/7] dax/hmem, cxl: Defer and resolve ownership of Soft
 Reserved memory ranges

Alejandro Lucero Palau wrote:
[..]
> I will take a look at this presentation, but I think there could be 
> another option where accelerators information is obtained during pci 
> enumeration by the kernel and using this information by this 
> functionality skipping those ranges allocated to them. Forcing them to 
> be compiled with the kernel would go against what distributions 
> currently and widely do with initramfs. Not sure if some current "early" 
> stubs could be used for this though but the information needs to be 
> recollected before this code does the checks.

The simple path is "do not use EFI_MEMORY_SP for accelerator memory".
However, if the accelerator wants to publish memory as EFI_MEMORY_SP
then it needs to coordinate with the kernel's default behavior somehow.
That means expanding the list of drivers that dax_hmem needs to await
before it can make a determination, or teaching dax_hmem to look for a
secondary indication that it should never fall back to the default
behavior.

Talk to your AMD peers Paul and Rajneesh about their needs. I took it on
faith that the use case was required.