linux-kernel - [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251219170538.1675743-2-gourry@gourry.net>
Date: Fri, 19 Dec 2025 12:05:37 -0500
From: Gregory Price <gourry@...rry.net>
To: linux-cxl@...r.kernel.org
Cc: linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	dave@...olabs.net,
	jonathan.cameron@...wei.com,
	dave.jiang@...el.com,
	alison.schofield@...el.com,
	vishal.l.verma@...el.com,
	ira.weiny@...el.com,
	dan.j.williams@...el.com,
	corbet@....net,
	gourry@...rry.net,
	rakuram.e96@...il.com,
	alucerop@....com
Subject: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update

Add a snippet about what Linux expects BIOS/EFI to do (and not
to do) to the BIOS/EFI section.

Suggested-by: Alejandro Lucero Palau <alucerop@....com>
Signed-off-by: Gregory Price <gourry@...rry.net>
---
 .../driver-api/cxl/platform/bios-and-efi.rst  | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
index a9aa0ccd92af..9034c206cf8e 100644
--- a/Documentation/driver-api/cxl/platform/bios-and-efi.rst
+++ b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
@@ -29,6 +29,26 @@ at :doc:`ACPI Tables <acpi>`.
    on physical memory region size and alignment, memory holes, HDM interleave,
    and what linux expects of HDM decoders trying to work with these features.
 
+
+Linux Expectations of BIOS/EFI Software
+=======================================
+Linux expects BIOS/EFI software to construct sufficient ACPI tables (such as
+CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA spaces
+and host-bridge interleave configurations) to allow the Linux driver to
+subsequently configure the devices in the CXL fabric at runtime.
+
+Programming of HDM decoders and switch ports is not required, and may be
+deferred to the CXL driver based on admin policy (e.g. udev rules).
+
+Some platforms may require pre-programming HDM decoders and locking them
+due to quirks (see: Zen5 address translation), but this is not the normal,
+"expected" configuration path.  This should be avoided if possible.
+
+Some platforms may wish to pre-configure these resources to bring memory
+up without requiring CXL driver support.  These platform vendors should
+test their configurations with the existing CXL driver and provide driver
+support for their auto-configurations if features like RAS are required.
+
 UEFI Settings
 =============
 If your platform supports it, the :code:`uefisettings` command can be used to
-- 
2.52.0