RE: [PATCH v2 08/10] iommufd/device: Use iommu_group_replace_domain()

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Wednesday, February 15, 2023 3:15 PM
> 
> But things will be out of control, if user space continues mapping
> something onto domain1's iopt for idev2, even after it is attached
> covertly to domain2's iopt by the replace routine. I wonder how
> kernel should handle this and keep the consistency between IOMMUFD
> objects and iommu_group.
> 

this is where I don't understand.

domain mapping just reflects what an address space has.

Take Qemu for example. w/o vIOMMU domain mappings is added/
removed according to the change in the GPA address space.

w/ vIOMMU then it is synced with guest page table.

why would userspace construct mappings for a specific device?

when device is moved from one domain to another domain, it just
bears with whatever the new domain allows it to access.