Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3

[Jason Gunthorpe]

On Fri, Jan 31, 2025 at 09:33:16AM +0000, Shameerali Kolothum Thodi wrote:

> And Qemu does some checking to make sure that the device is indeed associated
> with the specified phys-smmuv3.  This can be done going through the sysfs 
> path checking
> which is what I guess libvirt is currently doing to populate the topology. So 
> basically
> Qemu is just replicating that to validate again.

I would prefer that iommufd users not have to go out to sysfs..
 
> Or another option is extending the IOMMU_GET_HW_INFO IOCTL to return the phys
> smmuv3 base address which can avoid going through the sysfs.

It also doesn't seem great to expose a physical address. But we could
have an 'iommu instance id' that was a unique small integer?

Jason