Re: [PATCH v2 1/2] iommu/amd: Enable swiotlb in all cases

[Christoph Hellwig]

On Thu, Apr 07, 2022 at 02:31:44PM +0100, Robin Murphy wrote:
> FWIW it's also broken for another niche case where
> iommu_default_passthrough() == false at init, but the user later changes a
> 32-bit device's default domain type to passthrough via sysfs, such that it
> starts needing regular dma-direct bouncing.

Yeah.

We also have yet another issue:  swiotlb is not allocate if there is
no memory outside the 4GB physical address space.  I think I can fix
that easily after my swiotlb init series goes in, before that it
would be a bit of a mess spread over all the architectures.