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On the x86 platform, the int 3 instruction causes a breakpoint trap. For KVM, the Virtual CPUs can be configured to exit to the hypervisor on this trap, by enabling the flags KVM_GUESTDBG_ENABLE and KVM_GUESTDBG_USE_SW_BP (see KVM documentation). When the VM exits, I would like to step over the instruction and continue execution, without the guest VM being notified of the breakpoint trap.

I have tried the following:

  1. Enable KVM_GUESTDBG_USE_SW_BP and KVM_GUESTDBG_ENABLE, wait for the breakpoint trap exit to occur
  2. Disable KVM_GUESTDBG_USE_SW_BP and enable KVM_GUESTDBG_SINGLESTEP
  3. Resume the vCPU to step over the int 3 instruction and generate another VM exit
  4. enable KVM_GUESTDBG_USE_SW_BP and disable KVM_GUESTDBG_SINGLESTEP to continue normal execution

This approach however fails to isolate the debug breakpoint trap from the guest VM, and the guest OS will receive the exception. Enabling KVM_GUESTDBG_BLOCKIRQ does not prevent this either.

Upon the first generated VM exit, how does one correctly step over a software-induced breakpoint trap, without leaking the breakpoint trap to the guest VM?

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