linux-kernel - Re: [PATCH v4 3/3] iommu: Drop sw_msi from iommu

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Message-ID: <Z+GQw2A5nzoxfiHc@nvidia.com>
Date: Mon, 24 Mar 2025 10:05:07 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Nathan Chancellor <nathan@...nel.org>, <kevin.tian@...el.com>,
	<robin.murphy@....com>, <joro@...tes.org>, <will@...nel.org>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] iommu: Drop sw_msi from iommu_domain

On Mon, Mar 24, 2025 at 09:55:48AM -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@...62) (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.

Or it should return 0 just for "case IOMMU_COOKIE_NONE" doing a
passthrough for !CONFIG_IRQ_MSI_IOMMU configuration.

Thanks
Nicolin