Re: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged_domain helper

[Jason Gunthorpe]

On Fri, Mar 10, 2023 at 11:14:59AM +0100, Eric Auger wrote:
> Hi Nicolin,
> 
> On 3/9/23 11:53, Nicolin Chen wrote:
> > The nature of ITS virtualization on ARM is done via hypercalls, so kernel
> > handles all IOVA mappings for the MSI doorbell in iommu_dma_prepare_msi()
> > and iommu_dma_compose_msi_msg(). The current virtualization solution with
> > a 2-stage nested translation setup is to do 1:1 IOVA mappings at stage-1
> Note that if we still intend to use that trick there is a known issue at
> kernel side that needs to be fixed.
> 
> ARM DEN 0049E.b IORT specification mandates that when
> RMRs are present, the OS must preserve PCIe configuration
> performed by the boot FW.

This limitation doesn't seem necessary for this MSI stuff?

What is it for?

Jason