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Lukas Wunner d88dfb756d
agp/amd64: Check AGP Capability before binding to unsupported devices 
Since commit 172efbb403 ("AGP: Try unsupported AGP chipsets on x86-64
by default"), the AGP driver for AMD Opteron/Athlon64 CPUs has attempted
to bind to any PCI device possessing an AGP Capability.

Commit 6fd0248939 ("amd64-agp: Probe unknown AGP devices the right
way") subsequently reworked the driver to perform a bind attempt to
any PCI device (regardless of AGP Capability) and reject a device in
the driver's ->probe() hook if it lacks the AGP Capability.

On modern CPUs exposing an AMD IOMMU, this subtle change results in an
annoying message with KERN_CRIT severity:

  pci 0000:00:00.2: Resources present before probing

The message is emitted by the driver core prior to invoking a driver's
->probe() hook.  The check for an AGP Capability in the ->probe() hook
happens too late to prevent the message.

The message has appeared only recently with commit 3be5fa2366 (Revert
"iommu/amd: Prevent binding other PCI drivers to IOMMU PCI devices").
Prior to the commit, no driver could bind to AMD IOMMUs.

The reason for the message is that an MSI is requested early on for the
AMD IOMMU, which results in a call from msi_sysfs_create_group() to
devm_device_add_group().  A devres resource is thus attached to the
driver-less AMD IOMMU, which is normally not allowed, but presumably
cannot be avoided because requesting the MSI from a regular PCI driver
might be too late.

Avoid the message by once again checking for an AGP Capability *before*
binding to an unsupported device.  Achieve that by way of the PCI core's
dynid functionality.

pci_add_dynid() can fail only with -ENOMEM (on allocation failure) or
-EINVAL (on bus_to_subsys() failure).  It doesn't seem worth the extra
code to propagate those error codes out of the for_each_pci_dev() loop,
so simply error out with -ENODEV if there was no successful bind attempt.
In the -ENOMEM case, a splat is emitted anyway, and the -EINVAL case can
never happen because it requires failure of bus_register(&pci_bus_type),
in which case there's no driver probing of PCI devices.

Hans has voiced a preference to no longer probe unsupported devices by
default (i.e. set agp_try_unsupported = 0).  In fact, the help text for
CONFIG_AGP_AMD64 pretends this to be the default.  Alternatively, he
proposes probing only devices with PCI_CLASS_BRIDGE_HOST.  However these
approaches risk regressing users who depend on the existing behavior.

Fixes: 3be5fa2366 (Revert "iommu/amd: Prevent binding other PCI drivers to IOMMU PCI devices")
Reported-by: Fedor Pchelkin <pchelkin@ispras.ru>
Closes: https://lore.kernel.org/r/wpoivftgshz5b5aovxbkxl6ivvquinukqfvb5z6yi4mv7d25ew@edtzr2p74ckg/
Reported-by: Hans de Goede <hansg@kernel.org>
Closes: https://lore.kernel.org/r/20250625112411.4123-1-hansg@kernel.org/
Tested-by: Hans de Goede <hansg@kernel.org>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Hans de Goede <hansg@kernel.org>
Link: https://lore.kernel.org/r/b29e7fbfc6d146f947603d0ebaef44cbd2f0d754.1751468802.git.lukas@wunner.de
2025-07-09 07:23:09 +02:00
arch The delayed from_timer() API cleanup: 2025-06-08 11:33:00 -07:00
block treewide, timers: Rename from_timer() to timer_container_of() 2025-06-08 09:07:37 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto EFI updates for v6.16 2025-05-30 12:42:57 -07:00
Documentation Documentation: nouveau: Update GSP message queue kernel-doc reference 2025-06-13 16:46:35 +02:00
drivers agp/amd64: Check AGP Capability before binding to unsupported devices 2025-07-09 07:23:09 +02:00
fs The delayed from_timer() API cleanup: 2025-06-08 11:33:00 -07:00
include drm/sched: Increment job count before swapping tail spsc queue 2025-07-01 16:14:47 -07:00
init Rust changes for v6.16 2025-06-04 21:18:37 -07:00
io_uring io_uring-6.16-20250606 2025-06-06 13:09:03 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel The delayed from_timer() API cleanup: 2025-06-08 11:33:00 -07:00
lib 13 hotfixes. 6 are cc:stable and the remainder address post-6.15 issues 2025-06-06 21:45:45 -07:00
LICENSES LICENSES: add CC0-1.0 license text 2025-05-21 14:54:17 +02:00
mm treewide, timers: Rename from_timer() to timer_container_of() 2025-06-08 09:07:37 +02:00
net treewide, timers: Rename from_timer() to timer_container_of() 2025-06-08 09:07:37 +02:00
rust rust: drm: remove unnecessary imports 2025-07-05 13:01:59 +02:00
samples - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
scripts Kbuild updates for v6.16 2025-06-07 10:05:35 -07:00
security require gcc-8 and binutils-2.30 2025-05-31 08:16:52 -07:00
sound treewide, timers: Rename from_timer() to timer_container_of() 2025-06-08 09:07:37 +02:00
tools turbostat v2025.06.08 2025-06-08 11:44:41 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge branch 'kvm-lockdep-common' into HEAD 2025-05-28 06:29:17 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap fourteen smb3 client fixes, most smbdirect related 2025-06-08 10:20:21 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Update Christoph's Email address and make it consistent 2025-05-12 23:50:31 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS MAINTAINERS: Change habanalabs maintainer 2025-07-05 09:23:12 +02:00
Makefile Linux 6.16-rc1 2025-06-08 13:44:43 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.