Re: [PATCH v2 7/7] iommu/s390: flush queued IOVAs on RPCIT out of resource indication

Niklas Schnelle
2022-12-02T15:13:46Z

On Fri, 2022-12-02 at 10:42 -0400, Jason Gunthorpe wrote:
> On Fri, Dec 02, 2022 at 03:29:50PM +0100, Niklas Schnelle wrote:
>
> > @Robin @Joerg, if you are open to changing .iotlb_sync_map such that it
> > can return and error and then failing the mapping operation I think
> > this is a great approach. One advantage over the previous approach of
> > flushing the queue isthat this should work for the pure IOMMU API too.
>
> I think it is pretty important that the "pure" IOMMU API work with
> whatever your solution its, the iommu_domain implementation in a
> driver should not be sensitive to if the dma-iommu.c is operating the
> domain or something else.
>
> Jason

Agree. At the moment, i.e. with current mainline and even with the
IOMMU improvements in Joerg's queue, the IOMMU APIdoesn't work when the
hypervisor returns out-of-resource from the IOTLB flush (RPCIT). This
is currently only handled correctly in the arch/s390/pci/pci_dma.c DMA
API implementation. I think both handling this with a hidden/inlined
.iotlb_sync_map in s390_iommu_map_pages() or with an enhanced
.iotlb_sync_map that then must be able to return an error will fix this
shortcoming. The latter would be something like this commit I'm
currently testing with:

https://git.kernel.org/pub/scm/linux/kernel/git/niks/linux.git/commit/?h=dma_iommu_v3&id=a2aecd821fe3c5e2549946a68d8b07e05b288a9b

Thanks,
Niklas