linux-kernel - [PATCH v3 0/5] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL

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Message-ID: <20250930044757.214798-1-Smita.KoralahalliChannabasappa@amd.com>
Date: Tue, 30 Sep 2025 04:47:52 +0000
From: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To: <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: 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>, Yao Xingtao <yaoxt.fnst@...itsu.com>,
	Peter Zijlstra <peterz@...radead.org>, Greg KH <gregkh@...uxfoundation.org>,
	Nathan Fontenot <nathan.fontenot@....com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....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>, Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH v3 0/5] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL

This series aims to address long-standing conflicts between dax_hmem and
CXL when handling Soft Reserved memory ranges.

Reworked from Dan's patch:
https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git/patch/?id=ab70c6227ee6165a562c215d9dcb4a1c55620d5d

Previous work:
https://lore.kernel.org/all/20250715180407.47426-1-Smita.KoralahalliChannabasappa@amd.com/

Link to v2:
https://lore.kernel.org/all/20250930042814.213912-1-Smita.KoralahalliChannabasappa@amd.com/

To note:
I have dropped 6/6th patch from v1 based on discussion with Zhijian. This
patch series doesn't cover the case of DEV_DAX_HMEM=y and CXL=m, which
results in DEV_DAX_CXL being disabled.

In that configuration, ownership of the soft-reserved ranges is handled by
HMEM instead of being managed by CXL.

/proc/iomem for this case looks like below:

850000000-284fffffff : CXL Window 0
  850000000-284fffffff : region3
    850000000-284fffffff : Soft Reserved
      850000000-284fffffff : dax0.0
        850000000-284fffffff : System RAM (kmem)
2850000000-484fffffff : CXL Window 1
  2850000000-484fffffff : region4
    2850000000-484fffffff : Soft Reserved
      2850000000-484fffffff : dax1.0
        2850000000-484fffffff : System RAM (kmem)
4850000000-684fffffff : CXL Window 2
  4850000000-684fffffff : region5
    4850000000-684fffffff : Soft Reserved
      4850000000-684fffffff : dax2.0
        4850000000-684fffffff : System RAM (kmem)

Link to the patch and discussions on this:
https://lore.kernel.org/all/20250822034202.26896-7-Smita.KoralahalliChannabasappa@amd.com/

I would appreciate input on how best to handle this scenario efficiently.

Applies to mainline master.

v3 updates:
 - Fixed two "From".

v2 updates:
 - Removed conditional check on CONFIG_EFI_SOFT_RESERVE as dax_hmem
   depends on CONFIG_EFI_SOFT_RESERVE. (Zhijian)
 - Added TODO note. (Zhijian)
 - Included region_intersects_soft_reserve() inside CONFIG_EFI_SOFT_RESERVE
   conditional check. (Zhijian)
 - insert_resource_late() -> insert_resource_expand_to_fit() and
   __insert_resource_expand_to_fit() replacement. (Boris)
 - Fixed Co-developed and Signed-off by. (Dan)
 - Combined 2/6 and 3/6 into a single patch. (Zhijian).
 - Skip local variable in remove_soft_reserved. (Jonathan)
 - Drop kfree with __free(). (Jonathan)
 - return 0 -> return dev_add_action_or_reset(host...) (Jonathan)
 - Dropped 6/6.
 - Reviewed-by tags (Dave, Jonathan)

Dan Williams (4):
  dax/hmem, e820, resource: Defer Soft Reserved registration until hmem
    is ready
  dax/hmem: Request cxl_acpi and cxl_pci before walking Soft Reserved
    ranges
  dax/hmem: Use DEV_DAX_CXL instead of CXL_REGION for deferral
  dax/hmem: Defer Soft Reserved overlap handling until CXL region
    assembly completes

Smita Koralahalli (1):
  dax/hmem: Reintroduce Soft Reserved ranges back into the iomem tree

 arch/x86/kernel/e820.c    |   2 +-
 drivers/cxl/acpi.c        |   2 +-
 drivers/dax/Kconfig       |   2 +
 drivers/dax/hmem/device.c |   4 +-
 drivers/dax/hmem/hmem.c   | 128 ++++++++++++++++++++++++++++++++++----
 include/linux/ioport.h    |  13 +++-
 kernel/resource.c         |  92 +++++++++++++++++++++++----
 7 files changed, 213 insertions(+), 30 deletions(-)

-- 
2.17.1