Re: [PATCH v2 00/19] iommufd: Add VIOMMU infrastructure (Part-1)

[Nicolin Chen]

On Tue, Oct 01, 2024 at 10:48:15AM -0300, Jason Gunthorpe wrote:
> On Sun, Sep 29, 2024 at 03:19:42PM +0800, Yi Liu wrote:
> > > So their viommu HW concepts come along with a requirement that there
> > > be a fixed translation for the VM, which we model by attaching a S2
> > > HWPT to the VIOMMU object which get's linked into the IOMMU HW as
> > > the translation for the queue memory.
> > 
> > Is the mapping of the S2 be static? or it an be unmapped per userspace?
> 
> In principle it should be dynamic, but I think the vCMDQ stuff will
> struggle to do that

Yea. vCMDQ HW requires a setting of the physical address of the
base address to a queue in the VM's ram space. If the S2 mapping
changes (resulting a different queue location in the physical
memory), VMM should notify the kernel for a HW reconfiguration.

I wonder what all the user cases are, which can cause a shifting
of S2 mappings? VM migration? Any others?

Thanks
Nicolin