[PATCH RESEND v2] kunit: Enable PCI on UML without triggering WARN()

[Thomas Weißschuh]

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.

Signed-off-by: Thomas Weißschuh <thomas.w...@linutronix.de>
Reviewed-by: Johannes Berg <joha...@sipsolutions.net>
---
Changes in v2:
- Rebase onto v6.17-rc1
- Pick up review from Johannes
- Link to v1: https://lore.kernel.org/r/20250627-kunit-uml-p...@linutronix.de
---
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 c10ede4b1d2201d5f8cddeb71cc5096e21be9b6a..1823539e96da30e165fa8d395ccbd3f6754c836e 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 54ad8972681a2cc724e6122b19407188910b9025..28edf816aa70e6f408d9486efff8898df79ee090 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

---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20250626-kunit-uml-pci-a2b687553746

Best regards,
--
Thomas Weißschuh <thomas.w...@linutronix.de>

[Geert Uytterhoeven]

Hi Thomas,

On Mon, 8 Sept 2025 at 09:04, Thomas Weißschuh

<thomas.w...@linutronix.de> wrote:
> 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.
>
> Signed-off-by: Thomas Weißschuh <thomas.w...@linutronix.de>
> Reviewed-by: Johannes Berg <joha...@sipsolutions.net>

Thanks for your patch!

> --- 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

Where is the consumer of this symbol?

> + 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 54ad8972681a2cc724e6122b19407188910b9025..28edf816aa70e6f408d9486efff8898df79ee090 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

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds

[Thomas Weißschuh]

Hi Geert,

There is none. The relevant part is that it selects UML_PCI which on its own is
not user-visible. Directly enabling UML_PCI wihtout any drivers only makes
sense in the context of KUnit.

[David Gow]

On Mon, 8 Sept 2025 at 15:03, Thomas Weißschuh

<thomas.w...@linutronix.de> wrote:
>
> 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.
>
> Signed-off-by: Thomas Weißschuh <thomas.w...@linutronix.de>
> Reviewed-by: Johannes Berg <joha...@sipsolutions.net>
> ---

Reviewed-by: David Gow <davi...@google.com>

Cheers,
-- David

[Shuah Khan]

I am applying this patch for 6.18-rc1.

Please send a patch to fix the following warning on top of this one based
on

https://web.git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/log/?h=kunit

WARNING: please write a help paragraph that fully describes the config symbol with at least 4 lines
#136: FILE: lib/kunit/Kconfig:109:

+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.

thanks,
-- Shuah