Re: [RFC PATCH 0/12] iommu/riscv: Add nested translation (vIOMMU) support

[Jason Gunthorpe]

On Fri, Oct 16, 2026 at 05:16:10PM +0800, Gong Shuai wrote:
> Hi Jason,
> 
> Thanks for the review again.
> 
> > > Add nested translation support to the RISC-V IOMMU driver, so a KVM guest
> > > with its own vIOMMU can own the first stage of a device context while the
> > > host keeps the second stage, and add the interrupt support. This is an RFC
> > > and comments on the design are welcome.
> >
> > The iommufd parts looked reasonable to me
> >
> > I feel some mild skepticism about all the MSI parts, it would be good
> > to get more of the interrupt stuff actually landed before posting this
> > again.
> 
> Agreed on the MSI parts. They are a working proof to exercise the
> nested flow end to end, not a finished design. The reason they are
> in this series at all is that the NVMe device we use for testing
> depends on MSI interrupts. Without this support, DMA succeeds but
> the MSIs fault, so the driver ends up polling for completions after
> timeouts.
> 
> We will keep following the irqbypass groundwork as it evolves, and
> continue this work once it has landed.

It seems to me the riscv interrupt architecture is a terrible fit for
Linux, so I would prefer you keep that out of a viommu series and try
to address interrupt support in VFIO through the other series.

viommu shouldn't change anything about how interrupts work..

Without the msi stuff I think you could get this merged without a big
trouble.

Jason