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

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Message-ID: <CABVgOSmCNs2DQbyj=MAm-LHBRbEiCO1Adb-mSt+fbgOa8v4iYA@mail.gmail.com>
Date: Sat, 13 Sep 2025 14:14:18 +0800
From: David Gow <davidgow@...gle.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Brendan Higgins <brendan.higgins@...ux.dev>, Rae Moar <rmoar@...gle.com>, 
	Richard Weinberger <richard@....at>, Anton Ivanov <anton.ivanov@...bridgegreys.com>, 
	Johannes Berg <johannes@...solutions.net>, 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 Mon, 8 Sept 2025 at 15:03, Thomas Weißschuh
<thomas.weissschuh@...utronix.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.weissschuh@...utronix.de>
> Reviewed-by: Johannes Berg <johannes@...solutions.net>
> ---

Reviewed-by: David Gow <davidgow@...gle.com>

Cheers,
-- David

> 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.
> +
>  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.weissschuh@...utronix.de>
>