KVM: fix CPU reset wrt HF2_GIF_MASK

KVM: fix CPU reset wrt HF2_GIF_MASK

HF2_GIF_MASK is set in env->hflags2 unconditionally on CPU reset
(see x86_cpu_reset()) but when calling KVM_SET_NESTED_STATE,
KVM_STATE_NESTED_GIF_SET is only valid for nSVM as e.g. nVMX code
looks like

if (kvm_state->hdr.vmx.vmxon_pa == -1ull) {
    if (kvm_state->flags & ~KVM_STATE_NESTED_EVMCS)
        return -EINVAL;
}

Also, when adjusting the environment after KVM_GET_NESTED_STATE we
need not reset HF2_GIF_MASK on VMX as e.g. x86_cpu_pending_interrupt()
expects it to be set.

Alternatively, we could've made env->hflags2 SVM-only.

Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Fixes: b16c0e20c742 ("KVM: add support for AMD nested live migration")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200723142701.2521161-1-vkuznets@redhat.com>
Tested-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>