On 02/10/19 16:15, Jerome Glisse wrote: >>> Why would you need to target mmu notifier on target vma ? >> If the mapping of the source VMA changes, mirroring can update the >> target VMA via insert_pfn. But what ensures that KVM's MMU notifier >> dismantles its own existing page tables (so that they can be recreated >> with the new mapping from the source VMA)? >> > So just to make sure i follow we have: > - qemu process on host with anonymous vma > -> host cpu page table > - kvm which maps host anonymous vma to guest > -> kvm guest page table > - kvm inspector process which mirror vma from qemu process > -> inspector process page table > > AFAIK the KVM notifier's will clear the kvm guest page table whenever > necessary (through kvm_mmu_notifier_invalidate_range_start). This is > what ensure that KVM's dismatles its own mapping, it abides to mmu- > notifier callbacks. If you did not you would have bugs (at least i > expect so). Am i wrong here ? The KVM inspector process is also (or can be) a QEMU that will have to create its own KVM guest page table. So if a page in the source VMA is unmapped we want: - the source KVM to invalidate its guest page table (done by the KVM MMU notifier) - the target VMA to be invalidated (easy using mirroring) - the target KVM to invalidate its guest page table, as a result of invalidation of the target VMA Paolo
