[PATCH] iommu/io-pgtable-arm: Drop DMA API usage for CMOs

[Mostafa Saleh]

On Thu, Jan 8, 2026 at 12:59 PM Jason Gunthorpe <jgg at ziepe.ca> wrote:
>
> On Thu, Jan 08, 2026 at 11:38:46AM +0000, Mostafa Saleh wrote:
> > Jason pointed out that the DMA-API calls are not really needed [2].
> >
> > Looking more into this. Initially, the io-pgtable API let drivers
> > do the CMOs using tlb::flush_pgtable() where drivers were using the
> > DMA API (map/unmap_single) only to do CMOs as the low-level cache
> > functions won’t be available for modules.
>
> This isn't what I ment at all, the iommu-pages.h could do the flush
> inside itself using the already existing
> iommu_pages_flush_incoherent() instead of open coding the dma api
> calls everwhere, and maybe that could directly call the arch function
> on arm (as x86 does) which would be easier to implement in pkvm's
> hypervisor.
>

I see, so basically, we add the check for IOMMU_PAGES_USE_DMA_API in
iommu_pages_flush_incoherent() with the DMA-API stuff and call it from
the io-pgtable-arm instead.

> Then it is reasonable to have a pkvm version of the iommu-pages api
> for the page table and drive rto use.
>

That makes sense, I will look it over and send another version if
Robin is Ok with it.

Thanks,
Mostafa

> Jason