HV passes the return value of vmcall by register RAX unconditionally.
However, if the vmcall is undefined for a guest, RAX value of guest vcpu
should not be changed.
According to SDM Vol. 3C 30-9, VMCALL is allowed from any CPL in guest.
VMCALL is NOT allowed from CPL > 0 in vmx root mode.
ACRN hypervisor doesn't call VMCALL in vmx root mode, though.
In current code, ACRN also deny VMCALL from CPL > 0 in guest.
So for this case, #GP will not be injected, instead, modify the RAX to
notify the return value.
Tracked-On: #2405
Signed-off-by: Binbin Wu <binbin.wu@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>
2fd6e119ca