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In x86, there are two kinds of IO channels: Port-Based IO(aka '''PIO''' ) and Memory-Mapped IO(aka '''MMIO'''). PIO has separate address space and special instructions to do IO jobs. while with MMIO, the device IO space is backed with the memory address space, you can use memory data move instructions to do IO jobs.
==== PIO emulation ====
with Intel VT-x, the hypervisor is able to determine whether the guest's IO instructions trap into vmx root mode by setting the primary processor based control bit 24. if this bit is set, all the guest's IO instructions will causes vm exits. otherwise, you have to setup the two IO bitmap regions to capture the vm exits you are interested
the IO causes vm exit with basic reason number as 30, you can retrieve the IO operation size, direction, port id and etc. for more please refer to the vmx_pio.c in reference pages.
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2). search the MMIO devices regions to see whether the address is backed with a DEVICE.
3). store the result in destination register if necessary.
4). advance to next instruction by
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