[PATCH 09/11] selftests: cgroup: add a vmtest script for memcg

Following dmem's example[1], add a vmtest-memcg.sh to provide a
repeatable VM workflow using virtme-ng for memcg tests.

Boot a VM using virtme-ng with cma=64M in its kargs and enable
memory_cma_accounting on cgroupfs, then run the cgroup tests inside the
guest.

Provide -b to build the kernel first, -q to use a different qemu binary,
-s to start a shell in the VM, and -v for verbose boot.

[1] https://lore.kernel.org/all/[email protected]/

Signed-off-by: Eric Chanudet <[email protected]>
---
 tools/testing/selftests/cgroup/vmtest-memcg.sh | 196 +++++++++++++++++++++++++
 1 file changed, 196 insertions(+)

diff --git a/tools/testing/selftests/cgroup/vmtest-memcg.sh b/tools/testing/selftests/cgroup/vmtest-memcg.sh
new file mode 100755
index 000000000000..b19b96731784
--- /dev/null
+++ b/tools/testing/selftests/cgroup/vmtest-memcg.sh
@@ -0,0 +1,196 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (c) 2026 Red Hat, Inc.
+#
+# Run cgroup memory controller selftests inside a virtme-ng VM
+# Dependencies:
+#		* virtme-ng
+#		* busybox-static (used by virtme-ng)
+#		* qemu	(used by virtme-ng)
+
+set -euo pipefail
+
+readonly SCRIPT_DIR="$(cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
+readonly KERNEL_CHECKOUT="$(realpath "${SCRIPT_DIR}"/../../../../)"
+
+source "${SCRIPT_DIR}"/../kselftest/ktap_helpers.sh
+
+readonly SSH_GUEST_PORT="${SSH_GUEST_PORT:-22}"
+readonly WAIT_PERIOD=3
+readonly WAIT_PERIOD_MAX=80
+readonly WAIT_TOTAL=$((WAIT_PERIOD * WAIT_PERIOD_MAX))
+readonly QEMU_PIDFILE="$(mktemp /tmp/qemu_memcg_vmtest_XXXX.pid)"
+readonly QEMU_OPTS=" --pidfile ${QEMU_PIDFILE} "
+
+BUILD=0
+QEMU="qemu-system-$(uname -m)"
+VERBOSE=0
+SHELL_MODE=0
+GUEST_TREE="${GUEST_TREE:-$KERNEL_CHECKOUT}"
+
+usage() {
+	cat <<EOF
+$0 [OPTIONS]
+    -b        Build kernel from source tree before booting
+    -q <qemu> QEMU binary/path (default: $QEMU)
+    -s        Start interactive shell in VM
+    -v        Verbose output (vng boot logs on stdout)
+EOF
+	exit 1
+}
+
+die() {
+	echo "$*" >&2
+	exit "${KSFT_FAIL}"
+}
+
+cleanup() {
+	if [[ -s "$QEMU_PIDFILE" ]]; then
+		pkill -SIGTERM -F "$QEMU_PIDFILE" >/dev/null 2>&1 || true
+	fi
+
+	if [[ -e "$QEMU_PIDFILE" ]]; then
+		rm -f "$QEMU_PIDFILE"
+	fi
+}
+
+vm_ssh() {
+	stdbuf -oL ssh -q \
+		-F "$HOME/.cache/virtme-ng/.ssh/virtme-ng-ssh.conf" \
+		-l root "virtme-ng%$SSH_GUEST_PORT" \
+		"$@"
+}
+
+check_deps() {
+	for dep in vng "$QEMU" busybox pkill ssh; do
+		if ! command -v "$dep" >/dev/null 2>&1; then
+			echo "skip: dependency $dep not found"
+			exit "$KSFT_SKIP"
+		fi
+	done
+}
+
+handle_build() {
+	if [[ ! "$BUILD" -eq 1 ]]; then
+		return
+	fi
+
+	if [[ ! -d "$KERNEL_CHECKOUT" ]]; then
+		echo "-b requires $0 to be called from the kernel source tree" >&2
+		exit 1
+	fi
+
+	pushd "$KERNEL_CHECKOUT" &>/dev/null
+
+	if ! vng --kconfig --config "$SCRIPT_DIR"/config; then
+		die "failed to generate .config for kernel source tree ($KERNEL_CHECKOUT)"
+	fi
+
+	if ! make -j"$(nproc)"; then
+		die "failed to build kernel from source tree ($KERNEL_CHECKOUT)"
+	fi
+
+	popd &>/dev/null
+}
+
+vm_start() {
+	local logfile=/dev/null
+	local verbose_opt=""
+	local kernel_opt=""
+
+	if [[ "$VERBOSE" -eq 1 ]]; then
+		verbose_opt="--verbose"
+		logfile=/dev/stdout
+	fi
+
+	if [[ "$BUILD" -eq 1 ]]; then
+		kernel_opt="${KERNEL_CHECKOUT}"
+	fi
+
+	vng \
+		--run \
+		${kernel_opt} \
+		${verbose_opt} \
+		--qemu-opts="$QEMU_OPTS" \
+		--qemu="$(command -v "$QEMU")" \
+		--user root \
+		--ssh "$SSH_GUEST_PORT" \
+		--append "cma=64M" \
+		--rw &>"$logfile" &
+
+	local vng_pid=$!
+	local elapsed=0
+
+	while [[ ! -s "$QEMU_PIDFILE" ]]; do
+		kill -0 "$vng_pid" 2>/dev/null || \
+			die "vng exited early; failed to boot VM"
+		[[ "$elapsed" -ge "$WAIT_TOTAL" ]] && \
+			die "timed out waiting for VM boot"
+		sleep 1
+		elapsed=$((elapsed + 1))
+	done
+}
+
+vm_wait_for_ssh() {
+	local i=0
+	while true; do
+		vm_ssh -- true && break
+		i=$((i + 1))
+		[[ "${i}" -gt "$WAIT_PERIOD_MAX" ]] && \
+			die "timed out waiting for guest ssh"
+		sleep "$WAIT_PERIOD"
+	done
+}
+
+check_guest_requirements() {
+	vm_ssh -- "grep -q memory /sys/fs/cgroup/cgroup.controllers" \
+		|| die "memory controller not available (CONFIG_MEMCG?)"
+	vm_ssh -- "[[ -e /dev/dma_heap/default_cma_region ]]" \
+		|| die "CMA heap not available (CONFIG_DMABUF_HEAPS_CMA? cma= cmdline?)"
+}
+
+setup_guest_cma_accounting() {
+	vm_ssh -- "mount -o remount,memory_cma_accounting /sys/fs/cgroup" \
+		|| die "failed to enable memory_cma_accounting"
+	vm_ssh -- "echo +memory > /sys/fs/cgroup/cgroup.subtree_control" \
+		|| die "failed to enable memory controller"
+}
+
+run_test() {
+	vm_ssh -- "cd '$GUEST_TREE' && make -C tools/testing/selftests TARGETS=cgroup"
+	vm_ssh -- "cd '$GUEST_TREE' && make -C tools/testing/selftests TARGETS=cgroup run_tests"
+}
+
+while getopts ":hvq:sb" opt; do
+	case "$opt" in
+	v) VERBOSE=1 ;;
+	q) QEMU="${OPTARG}" ;;
+	b) BUILD=1 ;;
+	s) SHELL_MODE=1 ;;
+	h|*) usage ;;
+	esac
+done
+
+trap cleanup EXIT
+
+check_deps
+handle_build
+echo "Booting virtme-ng VM..."
+vm_start
+vm_wait_for_ssh
+echo "VM is reachable via SSH."
+
+if [[ "$SHELL_MODE" -eq 1 ]]; then
+	echo "Starting interactive shell in VM. Exit to stop VM."
+	vm_ssh -t -- "cd '$GUEST_TREE' && exec bash --noprofile --norc"
+	exit "$KSFT_PASS"
+fi
+
+check_guest_requirements
+setup_guest_cma_accounting
+
+echo "Running cgroup selftests in VM..."
+run_test
+echo "PASS: cgroup selftests completed"
+exit "$KSFT_PASS"

-- 
2.53.0