Re: [RFC PATCH kernel] iommufd: Allow mapping from KVM's guest_memfd

Sean Christopherson
2026-02-25T13:55:24Z

On Wed, Feb 25, 2026, Alexey Kardashevskiy wrote:
> For the new guest_memfd type, no additional reference is taken as
> pinning is guaranteed by the KVM guest_memfd library.
>
> There is no KVM-GMEMFD->IOMMUFD direct notification mechanism as
> the assumption is that:
> 1) page stage change events will be handled by VMM which is going
> to call IOMMUFD to remap pages;
> 2) shrinking GMEMFD equals to VM memory unplug and VMM is going to
> handle it.

The VMM is outside of the kernel's effective TCB. Assuming the VMM will always
do the right thing is a non-starter.