Comment 6 for bug 2071471

Hi Niklas, thanks for the backgrounds.

So to sum it up:

The Ubuntu kernel config options for IOMMU_DEFAULT_DMA_LAZY and IOMMU_DEFAULT_DMA_STRICT haven't changed since jammy/22.04:

5.15.0-1.1 to 5.15.0-115.125
CONFIG_IOMMU_DEFAULT_DMA_STRICT=y
# CONFIG_IOMMU_DEFAULT_DMA_LAZY is not set

6.8.0-6.6 to 6.8.0-38.38
CONFIG_IOMMU_DEFAULT_DMA_STRICT=y
# CONFIG_IOMMU_DEFAULT_DMA_LAZY is not set

But with the introduction of
c76c067e488c s390/pci: Use dma-iommu layer
which moves to a different dma-iommu implementation and
92bce97f0c34 s390/pci: Fix reset of IOMMU software counters
(both available since 6.7(rc-1)
the IOMMU_DEFAULT_DMA_LAZY kernel config option should be set to 'yes' by default for s390x.

Does CONFIG_IOMMU_DEFAULT_DMA_STRICT need to be set to No on top? I don't think so - if lazy is 'yes'.

So I believe we can go with 'IOMMU_DEFAULT_DMA_LAZY=y' for s390x only and should be good again.

I assume that such situations happen not very often,
so it would be ideal if IBM could give us a quick heads-up in such cases (where a kernel config default value for s390x is changed upstream), so that we can double check and potentially take over changes into the Ubuntu config by hand.