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

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Message-ID: <3dc95227-2be9-48a0-bdea-3f283d9b2a38@linuxfoundation.org>
Date: Mon, 15 Sep 2025 10:29:05 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 Brendan Higgins <brendan.higgins@...ux.dev>, David Gow
 <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
 Richard Weinberger <richard@....at>,
 Anton Ivanov <anton.ivanov@...bridgegreys.com>,
 Johannes Berg <johannes@...solutions.net>,
 Shuah Khan <skhan@...uxfoundation.org>
Cc: linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, linux-um@...ts.infradead.org
Subject: Re: [PATCH RESEND v2] kunit: Enable PCI on UML without triggering
 WARN()

On 9/8/25 01:03, Thomas Weißschuh 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.weissschuh@...utronix.de>
> Reviewed-by: Johannes Berg <johannes@...solutions.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-pci-v1-1-a622fa445e58@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.

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