On 21.07.19 21:14, Paolo Bonzini wrote: > On 21/07/19 19:40, Jan Kiszka wrote: >> Hi all, >> >> made some progress understanding why vmport from L2 breaks since QEMU gets/sets >> the nested state around it: We do not preserve VM_EXIT_INSTRUCTION_LEN, and that >> breaks skip_emulated_instruction when completing the PIO access on next run. The >> field is suddenly 0, and so we loop infinitely over the IO instruction. Unless >> some other magic prevents migration while an IO instruction is in flight, vmport >> may not be the only victim here. >> >> Now the question is how to preserve that information: Can we restore the value >> into vmcs02 on set_nested_state, despite this field being read-only? Or do we >> need to cache its content and use that instead in skip_emulated_instruction? > > Hmm I think technically this is invalid, since you're not supposed to > modify state at all while MMIO is pending. Of course that's kinda moot > if it's the only way to emulate vmport, but perhaps we can (or even > should!) fix it in QEMU. Is KVM_SET_NESTED_STATE needed for level < > KVM_PUT_RESET_STATE? Even if it is, we should first complete I/O and > then do kvm_arch_put_registers. Are we sure that vmport is the only case? What prevents a migration from starting in the middle of an IO exit? And I suspect we need to enhance the API specification then. Jan
