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On S3 path, we may transfer to long mode (if DXE is long mode) to restore CPU contexts with CR3 = SmmS3Cr3 (in SMM). AP will execute hlt-loop after CPU contexts restoration. Once one NMI or SMI happens, APs may exit from hlt state and execute the instruction after HLT instruction. If APs are running on long mode, page table is required to fetch the instruction. However, CR3 pointer to page table in SMM. APs will crash. This fix is to disable long mode on APs and transfer to 32bit protected mode to execute hlt-loop. Then CR3 and page table will no longer be required. https://bugzilla.tianocore.org/show_bug.cgi?id=216 Reported-by: Laszlo Ersek <lersek@redhat.com> Analyzed-by: Paolo Bonzini <pbonzini@redhat.com> Analyzed-by: Laszlo Ersek <lersek@redhat.com> Cc: Laszlo Ersek <lersek@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Jiewen Yao <jiewen.yao@intel.com> Cc: Michael D Kinney <michael.d.kinney@intel.com> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Jeff Fan <jeff.fan@intel.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Jiewen Yao <jiewen.yao@intel.com> Tested-by: Laszlo Ersek <lersek@redhat.com>