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

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Message-ID: <20250324204352.GA2734321@ax162>
Date: Mon, 24 Mar 2025 13:43:52 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, 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 05:05:01PM -0300, Jason Gunthorpe wrote:
> On Mon, Mar 24, 2025 at 10:07:43AM -0700, Nathan Chancellor wrote:
> 
> > 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;
> >  		}
> >  	}
> 
> Can we explain why this scenario has a 0 cookie_type?
> 
> Actually.. Is it just an identity domain? Nicolin did you test this on
> your arm system with a device using identity (iommu=pt kernel param)?
> I would expect identity to end up with a 0 cookie because we never
> setup dma-iommu.c code on it.
> 
> Should we be testing for identity to return 0 instead?

For the record, the particular system I noticed the issue on does need
"iommu.passthrough=1" (which is the ARM equivalent to "iommu=pt" IIUC?)
to boot due to a lack of firmware support for IORT RMR, so I think the
answer to your first question is probably yes?

Cheers,
Nathan