Re: [PATCH RFCv1 03/10] hw/arm/virt: Get the number of host-level SMMUv3 instances

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, Jul 09, 2024 at 11:20:16AM +0200, Eric Auger wrote:
> On 6/26/24 02:28, Nicolin Chen wrote:
> > Nested SMMUv3 feature requires the support/presence of host-level SMMUv3
> > instance(s). Add a helper to read the sysfs for the number of instances.
> > Log them in a vms list using a new struct VirtNestedSmmu.
> >
> > This will be used by a following patch to assign a passthrough device to
> > corresponding nested SMMUv3 instance.

> Laterly the HostIOMMUDevice has been introduced to allow, among other
> things, to pass information related to the physical IOMMU to the virtual
> IOMMU.
> I guess it would be well fitted to associate the viommu with its
> underlying piommu.

Wow, I missed that part -- backends/host_iommu_device. I will
see how I can fit these well with that.

> I don't think we have such kind of host introspection in machine type.
> Generally in can happen in the very device or in libvirt.

I think the biggest reason for having such an introspection in
the virt code is because of hotplug, (though it's not properly
implemented yet), as we don't know what new devices requiring
for nested translation would be joining later. So somebody has
to hold a full list.

Would you mind elaborating how the "device" or "libvirt" can
handle that?

Thanks!
Nicolin