Re: [PATCH v4 3/3] iommu: Drop sw_msi from iommu_domain

[Nathan Chancellor <nathan@kernel.org>]

On Mon, Mar 24, 2025 at 09:55:46AM -0700, Nicolin Chen wrote:
> On Mon, Mar 24, 2025 at 01:40:23PM -0300, Jason Gunthorpe wrote:
> > On Mon, Mar 24, 2025 at 09:25:58AM -0700, Nathan Chancellor wrote:
> > 
> > > I bisected a loss of networking on one of my machines to this change as
> > > commit e009e088d88e ("iommu: Drop sw_msi from iommu_domain") in -next.
> > 
> > Okay wow, I will drop this series from the tree if I don't see a
> > resolution in a few days. We can try again next cycle, thank you for
> > testing and bisect!
> > 
> > > At this change, I see:
> > > 
> > >   [  +0.000000] Linux version 6.14.0-rc2-00033-ge009e088d88e (nathan@ax162) (aarch64-linux-gcc (GCC) 14.2.0, GNU ld (GNU Binutils) 2.42) #1 SMP PREEMPT_DYNAMIC Mon Mar 24 08:57:49 MST 2025
> > >   ...
> > >   [  +0.002355] fsl_mc_bus NXP0008:00: Adding to iommu group 0
> > >   [  +0.000533] fsl_mc_bus NXP0008:00: MC firmware version: 10.28.1
> > >   [  +0.002565] fsl_mc_dprc dprc.1: DMA mask not set
> > >   [  +0.019255] fsl_mc_dprc dprc.1: Adding to iommu group 1
> > >   [  +0.046820] fsl_mc_dprc dprc.1: Failed to allocate IRQs
> > 
> > I guess it is tripping up going through iommu_dma_prepare_msi()
> > somehow?
> > 
> > Maybe fsl bus is special and doesn't manage to set
> > IOMMU_COOKIE_DMA_IOVA for some reason?
> > 
> > I wonder if this is not right:
> > 
> > +               default:
> > +                       ret = -EOPNOTSUPP;
> > +                       break;
> > 
> > And it should be just break instead (return 0) which is what was
> > happening before?
> 
> Yea, I found the diff here too.
> 
> Nathan, would you please give it a try by removing this
> 	ret = -EOPNOTSUPP;
> ?

Can confirm, I tested the following diff and it resolved my issue. If it
goes as a standalone patch:

Tested-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the quick triage!

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 0f4cc15ded1c..2b81166350ae 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3661,7 +3661,6 @@ int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
 			ret = iommufd_sw_msi(group->domain, desc, msi_addr);
 			break;
 		default:
-			ret = -EOPNOTSUPP;
 			break;
 		}
 	}