[PATCH AUTOSEL 6.17] kunit: Enable PCI on UML without triggering WARN()

[Sasha Levin]

From: Thomas Weißschuh <thomas.w...@linutronix.de>

[ Upstream commit 031cdd3bc3f369553933c1b0f4cb18000162c8ff ]

Various KUnit tests require PCI infrastructure to work. All normal
platforms enable PCI by default, but UML does not. Enabling PCI from
.kunitconfig files is problematic as it would not be portable. So in
commit 6fc3a8636a7b ("kunit: tool: Enable virtio/PCI by default on UML")
PCI was enabled by way of CONFIG_UML_PCI_OVER_VIRTIO=y. However
CONFIG_UML_PCI_OVER_VIRTIO requires additional configuration of
CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID or will otherwise trigger a WARN() in
virtio_pcidev_init(). However there is no one correct value for
UML_PCI_OVER_VIRTIO_DEVICE_ID which could be used by default.

This warning is confusing when debugging test failures.

On the other hand, the functionality of CONFIG_UML_PCI_OVER_VIRTIO is not
used at all, given that it is completely non-functional as indicated by
the WARN() in question. Instead it is only used as a way to enable
CONFIG_UML_PCI which itself is not directly configurable.

Instead of going through CONFIG_UML_PCI_OVER_VIRTIO, introduce a custom
configuration option which enables CONFIG_UML_PCI without triggering
warnings or building dead code.

Link: https://lore.kernel.org/r/20250908-kunit-uml-p...@linutronix.de
Signed-off-by: Thomas Weißschuh <thomas.w...@linutronix.de>
Reviewed-by: Johannes Berg <joha...@sipsolutions.net>
Reviewed-by: David Gow <davi...@google.com>
Signed-off-by: Shuah Khan <sk...@linuxfoundation.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES – this change removes a longstanding WARN() that currently fires on
every UML KUnit run while keeping the needed PCI plumbing available for
the tests.

- Default UML KUnit builds enable `CONFIG_UML_PCI_OVER_VIRTIO`, whose
probe path calls `WARN(CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID < 0, ...)`
and immediately bails out because the default device ID stays at -1
(arch/um/drivers/virtio_pcidev.c:616); many CI setups treat that WARN
as fatal, so KUnit runs are polluted or aborted.
- The patch introduces `CONFIG_KUNIT_UML_PCI` (lib/kunit/Kconfig:89) to
`select UML_PCI` directly when building UML with KUnit, letting us
obtain the PCI core helpers without instantiating the virtio shim that
never worked in this configuration anyway.
- With `tools/testing/kunit/configs/arch_uml.config:4` switching from
`CONFIG_VIRTIO_UML`/`CONFIG_UML_PCI_OVER_VIRTIO` to
`CONFIG_KUNIT_UML_PCI=y`, UML KUnit boots stop compiling the dead
`virtio_pcidev` code and therefore stop triggering the WARN while
still enabling the same PCI infrastructure the tests expect.
- The change is tightly scoped to KUnit-on-UML, introduces no behaviour
change for production kernels, and effectively fixes the regression
introduced by 6fc3a8636a7b (“kunit: tool: Enable virtio/PCI by default
on UML”).

lib/kunit/Kconfig | 7 +++++++
tools/testing/kunit/configs/arch_uml.config | 5 ++---
2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
index c10ede4b1d220..1823539e96da3 100644
--- a/lib/kunit/Kconfig
+++ b/lib/kunit/Kconfig
@@ -106,4 +106,11 @@ config KUNIT_DEFAULT_TIMEOUT
If unsure, the default timeout of 300 seconds is suitable for most
cases.

+config KUNIT_UML_PCI
+ bool "KUnit UML PCI Support"
+ depends on UML
+ select UML_PCI
+ help
+ Enables the PCI subsystem on UML for use by KUnit tests.
+
endif # KUNIT
diff --git a/tools/testing/kunit/configs/arch_uml.config b/tools/testing/kunit/configs/arch_uml.config
index 54ad8972681a2..28edf816aa70e 100644
--- a/tools/testing/kunit/configs/arch_uml.config
+++ b/tools/testing/kunit/configs/arch_uml.config
@@ -1,8 +1,7 @@
# Config options which are added to UML builds by default

-# Enable virtio/pci, as a lot of tests require it.
-CONFIG_VIRTIO_UML=y
-CONFIG_UML_PCI_OVER_VIRTIO=y
+# Enable pci, as a lot of tests require it.
+CONFIG_KUNIT_UML_PCI=y

# Enable FORTIFY_SOURCE for wider checking.
CONFIG_FORTIFY_SOURCE=y
--
2.51.0