[Bug 82211] [Nested xen on kvm] L1 guest panic and reboot when L1 guest boot up.

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https://bugzilla.kernel.org/show_bug.cgi?id=82211

--- Comment #1 from Zhou, Chao <chao.zhou@intel.com> ---
the first bad commit is:
commit 6addfc42992be4b073c39137ecfdf4b2aa2d487f
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Thu Mar 27 11:29:28 2014 +0100

    KVM: x86: avoid useless set of KVM_REQ_EVENT after emulation

    Despite the provisions to emulate up to 130 consecutive instructions, in
    practice KVM will emulate just one before exiting
handle_invalid_guest_state
    because x86_emulate_instruction always sets KVM_REQ_EVENT.

    However, we only need to do this if an interrupt could be injected,
    which happens a) if an interrupt shadow bit (STI or MOV SS) has gone
    away; b) if the interrupt flag has just been set (other instructions
    than STI can set it without enabling an interrupt shadow).

    This cuts another 700-900 cycles from the cost of emulating an
    instruction (measured on a Sandy Bridge Xeon: 1650-2600 cycles
    before the patch on kvm-unit-tests, 925-1700 afterwards).

    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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