KVM: nVMX: Disable vmcs02 posted interrupts if vmcs12 PID isn't mappable
Don't allow posted interrupts to modify a stale posted interrupt descriptor (including the initial value of 0). Empirical tests on real hardware reveal that a posted interrupt descriptor referencing an unbacked address has PCI bus error semantics (reads as all 1's; writes are ignored). However, kvm can't distinguish unbacked addresses from device-backed (MMIO) addresses, so it should really ask userspace for an MMIO completion. That's overly complicated, so just punt with KVM_INTERNAL_ERROR. Don't return the error until the posted interrupt descriptor is actually accessed. We don't want to break the existing kvm-unit-tests that assume they can launch an L2 VM with a posted interrupt descriptor that references MMIO space in L1. Fixes: 6beb7bd5 ("kvm: nVMX: Refactor nested_get_vmcs12_pages()") Signed-off-by: Jim Mattson <jmattson@google.com> Message-Id: <20210604172611.281819-8-jmattson@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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