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    SubjectRe: [RFC PATCH 00/35] SEV-ES hypervisor support
    On Mon, Nov 30, 2020, Paolo Bonzini wrote:
    > On 16/09/20 02:19, Sean Christopherson wrote:
    > >
    > > TDX also selectively blocks/skips portions of other ioctl()s so that the
    > > TDX code itself can yell loudly if e.g. .get_cpl() is invoked. The event
    > > injection restrictions are due to direct injection not being allowed (except
    > > for NMIs); all IRQs have to be routed through APICv (posted interrupts) and
    > > exception injection is completely disallowed.
    > >
    > > kvm_vcpu_ioctl_x86_get_vcpu_events:
    > > if (!vcpu->kvm->arch.guest_state_protected)
    > > events->interrupt.shadow = kvm_x86_ops.get_interrupt_shadow(vcpu);
    >
    > Perhaps an alternative implementation can enter the vCPU with immediate exit
    > until no events are pending, and then return all zeroes?

    This can't work. If the guest has STI blocking, e.g. it did STI->TDVMCALL with
    a valid vIRQ in GUEST_RVI, then events->interrupt.shadow should technically be
    non-zero to reflect the STI blocking. But, the immediate exit (a hardware IRQ
    for TDX guests) will cause VM-Exit before the guest can execute any instructions
    and thus the guest will never clear STI blocking and never consume the pending
    event. Or there could be a valid vIRQ, but GUEST_RFLAGS.IF=0, in which case KVM
    would need to run the guest for an indeterminate amount of time to wait for the
    vIRQ to be consumed.

    Tangentially related, I haven't looked through the official external TDX docs,
    but I suspect that vmcs.GUEST_RVI is listed as inaccessible for production TDs.
    This will be changed as the VMM needs access to GUEST_RVI to handle
    STI->TDVMCALL(HLT), otherwise the VMM may incorrectly put the vCPU into a
    blocked (not runnable) state even though it has a pending wake event.

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