Add network driver VM example

examples/eth_driver_vm/Makefile

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+#
+# Copyright 2025, UNSW
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+BUILD_DIR ?= build
+export MICROKIT_CONFIG ?= debug
+
+ifeq ($(strip $(MICROKIT_SDK)),)
+$(error MICROKIT_SDK must be specified)
+endif
+override MICROKIT_SDK := $(abspath $(MICROKIT_SDK))
+
+ifeq ($(strip $(MICROKIT_BOARD)),)
+$(error MICROKIT_BOARD must be specified)
+endif
+
+export BUILD_DIR := $(abspath $(BUILD_DIR))
+export EXAMPLE_DIR := $(abspath .)
+
+export TARGET := aarch64-none-elf
+export CC := clang
+export LD := ld.lld
+export AS := llvm-as
+export AR := llvm-ar
+export DTC := dtc
+export RANLIB := llvm-ranlib
+export MICROKIT_TOOL ?= $(MICROKIT_SDK)/bin/microkit
+export SDDF := $(abspath ../../dep/sddf)
+export LIBVMM := $(abspath ../../)
+export LIBVMM_TOOLS := ${LIBVMM}/tools
+export CC_USERLEVEL := zig cc
+
+IMAGE_FILE := $(BUILD_DIR)/loader.img
+REPORT_FILE := $(BUILD_DIR)/report.txt
+
+export ECHO_INCLUDE := $(SDDF)/examples/echo_server/include
+
+all: $(IMAGE_FILE)
+
+$(IMAGE_FILE) $(REPORT_FILE) clean clobber: $(BUILD_DIR)/Makefile FORCE
+	$(MAKE) -C $(BUILD_DIR) MICROKIT_SDK=$(MICROKIT_SDK) $(notdir $@)
+
+$(BUILD_DIR)/Makefile: echo.mk
+	mkdir -p $(BUILD_DIR)
+	cp echo.mk $@
+
+FORCE:

examples/eth_driver_vm/README.md

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+<!--
+     Copyright 2025, UNSW
+     SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
+# Ethernet Driver VM Example
+
+This example demonstrates an Ethernet driver VM running with sDDF's echo server on the Odroid C4. It is
+a shallow copy that only contains files that needs to be modified to accomodate the Ethernet driver
+VM.
+
+The only files that we copied from the echo server is `echo.mk` and `meta.py` to accomodate the VM.
+
+The idea is we have a userspace program in Linux that converts sDDF's network TX/RX into
+corresponding syscalls in a Linux raw socket.
+- The sDDF network control, data regions and notification from virtualisers are mapped into Linux
+  userspace via UIO.
+- A promiscuous socket is opened to sniff all incoming frames. When a frame comes through from the
+  socket, we enqueue the data into the appropriate sDDF queues and fault on a pre-determined address
+  so the VMM can notify the RX virtualiser.
+- When a client wants to transmit data, we will get TX virt notifications via UIO, then we simply
+  write the data out into the socket.
+
+Even though we already have a native Ethernet driver for Odroid C4, this example is still useful as
+it could be used to provide Ethernet driver VM on new boards or further developed into a
+WiFi/Cellular/Bluetooth driver VM.
+
+The example currently works on the following platforms:
+* HardKernel Odroid-C4
+
+Things to note when using the network UIO driver:
+- You need to map in the control queues as uncached in the guest and native virtualisers. This is
+  because Linux treats UIO regions as device memory thus map them uncached to userspace.
+
+## Compilation
+To compile this example, run:
+```
+make MICROKIT_SDK=<absolute path to SDK> MICROKIT_BOARD=odroidc4 MICROKIT_CONFIG=release
+```
+
+### Boot
+On a successful boot, your console will look like this:
+```
+1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
+    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
+2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq qlen 1000
+    link/ether 00:1e:06:4a:35:e4 brd ff:ff:ff:ff:ff:ff
+[    3.716293] meson8b-dwmac ff3f0000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off
+[    5.753497] random: crng init done
+UIO(NET): *** Starting up
+UIO(NET): *** Network interface: eth0
+UIO(NET): *** Setting up raw promiscuous socket
+[   10.669821] meson8b-dwmac ff3f0000.ethernet eth0: entered promiscuous mode
+UIO(NET): *** Creating epoll
+UIO(NET): *** Binding socket to epoll
+UIO(NET): *** Setting up data passing page via UIO
+UIO(NET): -> mapped device 'uio0' with size 0x1000 @ 0xffff8454d000
+UIO(NET): -> rx data paddr = 0x5feff000
+UIO(NET): -> tx client #0 data paddr = 0x5fdff000
+UIO(NET): -> tx client #1 data paddr = 0x5fcff000
+UIO(NET): *** Setting up in sDDF net control queues
+UIO(NET): -> mapped device 'uio1' with size 0x3000 @ 0xffff8454a000
+UIO(NET): -> mapped device 'uio3' with size 0x3000 @ 0xffff84547000
+UIO(NET): -> mapped device 'uio2' with size 0x5000 @ 0xffff84542000
+UIO(NET): -> mapped device 'uio4' with size 0x5000 @ 0xffff8453d000
+UIO(NET): *** Setting up TX/RX fault mechanism for guest -> VMM notifications
+UIO(NET): -> mapped device 'uio5' with size 0x1000 @ 0xffff8453c000
+UIO(NET): -> mapped device 'uio6' with size 0x1000 @ 0xffff8453b000
+UIO(NET): *** Setting up TX/RX UIO IRQs for VMM -> guest notifications
+UIO(NET): *** Binding UIO TX and RX incoming interrupts to epoll
+UIO(NET): *** Setting up in sDDF net data queues
+UIO(NET): -> mapped device 'uio9' with size 0x100000 @ 0xffff8443b000
+UIO(NET): -> mapped device 'uio10' with size 0x200000 @ 0xffff8423b000
+UIO(NET): *** All initialisation successful, now sending all pending TX active before we block on events
+UIO(NET): *** All pending TX active have been sent thru the raw sock, entering event loop now.
+UIO(NET): *** You won't see any output from UIO Net anymore. Unless there is a warning or error.
+DHCP request finished, IP address for netif client0 is: 172.16.1.91
+DHCP request finished, IP address for netif client1 is: 172.16.1.90
+```
+
+Though the MAC, IP and memory addreses would be different of course. There will be delay in the tens
+of seconds between the Linux userspace network driver initialisation and lwIP DHCP completion. This
+is due to all the components being able to initialise first before the guest can get to userspace.
+So lwIP will send many DHCP requests without success, with increasing timeout for each request.
+
+## Future work
+- Support more platforms.
+- Fix the avalance of:
+`<<seL4(CPU 0) [handleInterruptEntry/56 T0x8003849400 "net_driver_vm" @20c0fc]: Spurious interrupt!>>`
+on debug config.
+- Further minimise the Linux kernel. I've reduced the kernel size to only 12.5MiB by disabling most
+  drivers. Though there are room to push it further by disabling more features that we don't need.
+- Move the UIO driver into a kernel module or use iouring to reduce the context switch cost every
+  time we send or receive a frame.
+- (Tying into previous) Move away from UIO, which allow us to use SIMD instructions for faster
+  memory operations in the driver. I mentioned this as the network queue entry size isn't a power of
+  2, so clang always generate vector loads and stores to speed things up. Which has to be disabled
+  to make UIO happy.
+- Investigate mapping the queue and data regions as cached.
+- Properly implement WFI/WFE in libvmm so we correctly measure CPU utilisation.

examples/eth_driver_vm/board/odroidc4/README.md

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+<!--
+     Copyright 2024, UNSW
+     SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
+# Odroid-C4 images
+
+## Linux kernel
+
+### Details
+* Image name: `linux`
+* Config name: `linux_config`
+* Git remote: https://github.com/torvalds/linux.git
+* Tag: v6.17 (commit hash: `e5f0a698b34ed76002dc5cff3804a61c80233a7a`)
+* Toolchain: `aarch64-none-elf`
+    * Version: (Arm GNU Toolchain 12.2.Rel1 (Build arm-12.24)) 12.2.1 20221205
+
+You can also get the Linux config used after booting by running the following
+command in userspace: `zcat /proc/config.gz`.
+
+### Instructions for reproducing
+
+```
+git clone --depth 1 --branch v6.17 https://github.com/torvalds/linux.git
+cp linux_config linux/.config
+make -C linux ARCH=arm64 CROSS_COMPILE=aarch64-none-elf- linux_config all -j$(nproc)
+```
+
+The path to the image will be: `linux/arm64/boot/Image`.
+
+## Buildroot RootFS image
+
+Note that buildoot currently does not list a configuration for OdroidC4 so we just
+use the OdroidC2 configuration with `ethtool` enabled.