Small hands-on project for the class in Advanced OS at Scuola Superiore Sant'Anna held by Prof. L. Abeni [1]. The project expands a "hello world" example for KVM virtualization [2] by adding two simple I/O devices: a serial port, and a simple "disk". Other improvements over the starting example are:
- guest code is loaded from file
- fix bug in guest memory allocation (
aligned_allocarguments are swapped!) - guest code is compiled from C
By compiling with MMIO=true you can use memory-mapped I/O instead of port I/O.
[1] http://retis.santannapisa.it/luca/SOAvanzati/ [2] http://retis.santannapisa.it/luca/SOAvanzati/Src/kvm-test.tgz
make # compiles the code (port I/O)
# or `make MMIO=true`
make disk # creates empty disk (8KiB)
./test # runs hypervisor and guest
The serial port makes it possible to send messages from the guest to the host. These messages will be print to stdout by the vmm.
| port | direction | description |
|---|---|---|
| 0x10 | out | write the payload to the serial port |
The "disk" is a device which loads disk sectors (512B) to the VM memory through DMA and is controlled by three IO ports:
- the first sets the sector (512B) offset.
- the second sets the memory address for the DMA
- the third sends the operation to perform (0: read; 1: write, 2: setup)
The three operations are defined as follows:
- read: copy one sector (512B) from the "disk" to the address specified
- write: copy one sector (512B) from the address to the disk sector specified
- setup: create the disk status structure at the specified address
The status structure contains information about:
- disk size
- last operation error
The setup operation must be called before any other operation and may be called only once. The status structure will be updated by the host in place.
| port | direction | description |
|---|---|---|
| 0x20 | out | sets the offset of the disk (dword) |
| 0x21 | out | sets the offset in the guest memory for DMA (dword) |
| 0x22 | out | operation code (byte) |