On Wed, Jul 23, 2025, Vishal Annapurve wrote: > 2) Userspace brings a mappable guest_memfd to back guest private > memory (passed as guest_memfd field in the > KVM_USERSPACE_MEMORY_REGION2): KVM will always fault in all guest > faults via guest_memfd so if userspace brings in VMAs that point to > different physical memory then there would be a discrepancy between > what guest and userspace/KVM (going through HVAs) sees for shared > memory ranges. I am not sure if KVM needs to enforce anything here, We agreed (I think in a guest_memfd call?) that KVM won't enforce anything, because trying to do so for uaccesses, e.g. via __kvm_read_guest_page(), would require grabbing mmap_lock in hot paths, i.e. would be a complete non-starter. So yeah, it's the VMM's responsibility to not be stupid.
