KVM: selftests: nSVM: Add svm_nested_soft_inject_test

Add a KVM self-test that checks whether a nSVM L1 is able to successfully
inject a software interrupt, a soft exception and a NMI into its L2 guest.

In practice, this tests both the next_rip field consistency and
L1-injected event with intervening L0 VMEXIT during its delivery:
the first nested VMRUN (that's also trying to inject a software interrupt)
will immediately trigger a L0 NPF.
This L0 NPF will have zero in its CPU-returned next_rip field, which if
incorrectly reused by KVM will trigger a #PF when trying to return to
such address 0 from the interrupt handler.

For NMI injection this tests whether the L1 NMI state isn't getting
incorrectly mixed with the L2 NMI state if a L1 -> L2 NMI needs to be
re-injected.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
[sean: check exact L2 RIP on first soft interrupt]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <d5f3d56528558ad8e28a9f1e1e4187f5a1e6770a.1651440202.git.maciej.szmigiero@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>