Receive an IPI Communication

This section describes how a destination agent receives an IPI communication message. The destination agent accesses its IPI registers.

1. Prepare to receive a message request with one of the following steps.
   1. Enable the interrupt from the sender using the IPI mask register, IMR, and in the processor's system interrupt controller by accessing its GIC registers.
   2. Destination agent polls its IPI status register for bits being set.
2. When an interrupt is received, optionally write a 32-byte response into the appropriate message buffer.
3. Signal to the source agent that the interrupt has been processed with one of the following steps.
   1. Clear the destination IPI status register.
   2. Issue an IPI interrupt back to the source agent.