Re: [RFC PATCH 2/6] selftests/vfio: add sPAPR TCE v2 IOMMU mode

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The fallback default IOMMU mode remains hardcoded to MODE_IOMMUFD, causing test suites to crash out-of-the-box on PowerPC where IOMMUFD is not supported for VFIO.
--

commit 8dfc3e7df9b7153c07746fbc4679447d70174937
Author: Narayana Murty N <nnmlinux@linux.ibm.com>

selftests/vfio: add sPAPR TCE v2 IOMMU mode

Add a PowerPC-specific VFIO selftest IOMMU mode for sPAPR TCE v2.
The new mode uses the legacy VFIO container interface with
VFIO_SPAPR_TCE_v2_IOMMU.

[ ... ]

> diff --git a/tools/testing/selftests/vfio/lib/iommu.c b/tools/testing/selftests/vfio/lib/iommu.c
> index 035dac069d601..e86457a715bf7 100644
> --- a/tools/testing/selftests/vfio/lib/iommu.c
> +++ b/tools/testing/selftests/vfio/lib/iommu.c
> @@ -47,6 +47,13 @@ static const struct iommu_mode iommu_modes[] = {
>  	{
>  		.name = MODE_IOMMUFD,
>  	},
> +#ifdef __powerpc__
> +	{
> +		.name = MODE_VFIO_SPAPR_TCE_V2_IOMMU,
> +		.container_path = "/dev/vfio/vfio",
> +		.iommu_type = VFIO_SPAPR_TCE_v2_IOMMU,
> +	},
> +#endif
>  };

[Severity: Medium]
Since default_iommu_mode remains hardcoded to MODE_IOMMUFD earlier in this
file, does this cause test suites like vfio_pci_driver_test to crash
out-of-the-box on PowerPC systems?

For instance, device_has_selftests_driver() uses this default mode directly
before checking platform-specific fixtures:

tools/testing/selftests/vfio/vfio_pci_driver_test.c:device_has_selftests_driver() {
    ...
    iommu = iommu_init(default_iommu_mode);
    ...
}

If /dev/iommu cannot be opened or device bindings fail on PowerPC because
IOMMUFD isn't supported, does this trigger a failed assertion
(VFIO_ASSERT_GT(iommu->iommufd, 0)) and abort execution rather than
skipping gracefully?

Should default_iommu_mode be conditionally defined for PowerPC to use
MODE_VFIO_SPAPR_TCE_V2_IOMMU as the default fallback?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260703032806.40946-1-nnmlinux@linux.ibm.com?part=2