OS may enable CET-IBT feature by set MSR IA32_U_CET.bit2.
If IA32_U_CET.bit2 is set, CPU is in WAIT_FOR_ENDBRANCH state and
the next assemble code is not ENDBR, it will trigger #CP exception
when set CR4.CET bit.
SMI handler needs to backup MSR IA32_U_CET and clear MSR IA32_U_CET
before set CR4.CET bit,
And SMI handler needs to restore MSR IA32_U_CET when exit SMI handler.
Signed-off-by: Sheng Wei <w.sheng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Cc: Tan Dun <dun.tan@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
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