[BUG] VFIO on POWER9 / QEMU fails to allocate 32-bit DMA

On Linux 6.18, and potentially earlier Linux versions, attempting to pass through any PCI device via VFIO that requires 32-bit DMA results in the following error in the guest VM:

[   11.705413] cx23885 0000:00:02.0: Warning: IOMMU offset too big for device mask
[   11.709245] cx23885 0000:00:02.0: mask: 0xffffffff, table offset: 0x800000000000000

The same devices work correctly on the host kernel.  It appears that somehow 32-bit DMA is not available within a pSeries guest on a PowerNV host.