KVM: SEV: Prohibit migration of a VM that has mirrors
VMs that mirror an encryption context rely on the owner to keep the ASID allocated. Performing a KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM would cause a dangling ASID: 1. copy context from A to B (gets ref to A) 2. move context from A to L (moves ASID from A to L) 3. close L (releases ASID from L, B still references it) The right way to do the handoff instead is to create a fresh mirror VM on the destination first: 1. copy context from A to B (gets ref to A) [later] 2. close B (releases ref to A) 3. move context from A to L (moves ASID from A to L) 4. copy context from L to M So, catch the situation by adding a count of how many VMs are mirroring this one's encryption context. Fixes: 0b020f5a ("KVM: SEV: Add support for SEV-ES intra host migration") Message-Id: <20211123005036.2954379-11-pbonzini@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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