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

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Message-ID: <e1efbbd827e34800bd7fb0ea687645cc6c65e1ab.camel@linux.ibm.com>
Date: Wed, 27 Sep 2023 15:20:07 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Joerg Roedel <joro@...tes.org>
Cc: Jason Gunthorpe <jgg@...pe.ca>, Matthew Rosato <mjrosato@...ux.ibm.com>,
        Will Deacon <will@...nel.org>, Wenjia Zhang <wenjia@...ux.ibm.com>,
        Robin
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        Heiko Carstens
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        Alexander Gordeev
 <agordeev@...ux.ibm.com>,
        Christian Borntraeger
 <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Suravee
 Suthikulpanit <suravee.suthikulpanit@....com>,
        Hector Martin
 <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
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        Thierry
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        Krishna Reddy <vdumpa@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
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Subject: Re: [PATCH v12 0/6] iommu/dma: s390 DMA API conversion and
 optimized IOTLB flushing

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