Re: [PATCH v12 0/6] iommu/dma: s390 DMA API conversion and optimized IOTLB flushing

Niklas Schnelle
2023-09-27T13:21:03Z

On Wed, 2023-09-27 at 13:24 +0200, Niklas Schnelle wrote:
> On Wed, 2023-09-27 at 11:55 +0200, Joerg Roedel wrote:
> > Hi Niklas,
> >
> > On Wed, Sep 27, 2023 at 10:55:23AM +0200, Niklas Schnelle wrote:
> > > The problem is that something seems to be broken in the iommu/core
> > > branch. Regardless of whether I have my DMA API conversion on top or
> > > with the base iommu/core branch I can not use ConnectX-4 VFs.
> >
> > Have you already tried to bisect the issue in the iommu/core branch?
> > The result might sched some light on the issue.
> >
> > Regards,
> >
> > Joerg
>
> Hi Joerg,
>
> Working on it, somehow I must have messed up earlier. It now looks like
> it might in fact be caused by my DMA API conversion rebase and the
> "s390/pci: Use dma-iommu layer" commit. Maybe there is some interaction
> with Jason's patches that I haven't thought about. So sorry for any
> wrong blame.
>
> Thanks,
> Niklas

Hi,

I tracked the problem down from mlx5_core's alloc_cmd_page() via
dma_alloc_coherent(), ops->alloc, iommu_dma_alloc_remap(), and
__iommu_dma_alloc_noncontiguous() to a failed iommu_dma_alloc_iova().
The allocation here is for 4K so nothing crazy.

On second look I also noticed:

nvme 2007:00:00.0: Using 42-bit DMA addresses

for the NVMe that is working. The problem here seems to be that we set
iommu_dma_forcedac = true in s390_iommu_probe_finalize() because we
have currently have a reserved region over the first 4 GiB anyway so
will always use IOVAs larger than that. That however is too late since
iommu_dma_set_pci_32bit_workaround() is already checked in
__iommu_probe_device() which is called just before ops-
>probe_finalize(). So I moved setting iommu_dma_forcedac = true to
zpci_init_iommu() and that gets rid of the notice for the NVMe but I
still get a failure of iommu_dma_alloc_iova() in
__iommu_dma_alloc_noncontiguous(). So I'll keep digging.

Thanks,
Niklas