modules/kernel/README.md

@@ -1,9 +1,9 @@
 # kernel
 
-The kernel's run-time settings on a machine (novox/hq to-be 42 Phase 1, row 11). It holds two things:
-**transparent huge pages**, set per machine, and **the fallback kernel** (`linux-lts` with its headers) and
-its place on the boot menu (novox/hq ADR 0508 §9 and §10). The default kernel's package, and microcode, are
-not built yet.
+The kernel's run-time settings on a machine (novox/hq to-be 42 Phase 1, row 11). It holds three things:
+**transparent huge pages**, set per machine, **the fallback kernel** (`linux-lts` with its headers) and
+its place on the boot menu (novox/hq ADR 0508 §9 and §10), and **microcode** in every initramfs (novox/hq issue 1977).
+The default kernel's package is not built yet.
 
 ## Why (novox/hq issue 746)
 
@@ -53,6 +53,25 @@ built for the fallback kernel too) after its boot-entries service, so the entry
 | file | `/etc/pacman.d/hooks/90-mesh-kernel-boot-entries.hook` | runs the script after a kernel image is installed, upgraded or removed |
 | packages | `linux-lts`, `linux-lts-headers` | declared after the service and the hook |
 
+## Microcode in every initramfs (novox/hq issue 1977)
+
+Before this, `amd-ucode` was installed by hand on two machines and no initramfs carried it, so a machine booted from
+its default entry ran the CPU's older microcode (one machine: revision 0x0a201016 while the package held 0x0a20102e). The module
+declares the packages and makes mkinitcpio's own `microcode` hook part of every image, so every boot entry loads it,
+a default entry written by hand included, and no entry is edited. The fallback entry's own microcode lines stay (a second
+early archive is harmless).
+
+| | what | notes |
+|---|---|---|
+| packages | `amd-ucode`, `intel-ucode` | both on every machine; the `autodetect` hook keeps only the running CPU's microcode in the default image |
+| file | `/etc/mkinitcpio.conf.d/mesh-microcode.conf` | read by mkinitcpio after `mkinitcpio.conf`: appends `microcode` to `HOOKS` unless it names it |
+| file | `${dir:state}/initramfs` | the script, `apply`: when the drop-in differs from the one the images were last built with (`${dir:state}/initramfs-built`) it runs `mkinitcpio -P` and then records the drop-in; otherwise it says "as it was". Before building it takes a preset's `ALL_config="/etc/mkinitcpio.conf"` line out (that line makes mkinitcpio skip `mkinitcpio.conf.d`; a copy of the preset goes to `${dir:state}/taken-over/`; another `ALL_config` is left and named); after building, an image without `kernel/x86/microcode/` in its first 64 KiB fails the unit, which names it. A failed mkinitcpio fails the unit, says so and records nothing |
+| file | `/etc/systemd/system/mesh-kernel-initramfs.service` | oneshot, sandboxed: the file system read-only but for `/boot`, `/etc/mkinitcpio.d` and the module's state, a private `/tmp`, no home, no network |
+| service | `mesh-kernel-initramfs.service` | running and enabled; restarted when the unit, the script or the drop-in changes. Later kernel upgrades build their images through the distribution's own hook, with the drop-in in place |
+
+The module does not reboot: a machine loads the new microcode at its next boot. `kernel_boot` says the revision the CPU
+runs now and which images carry microcode.
+
 ## Kernel modules at boot, and the running kernel's modules kept
 
 A machine that runs for weeks meets a kernel upgrade that removes `/usr/lib/modules/<the running kernel>`: from then on
@@ -73,13 +92,13 @@ module says so in its health and takes no image build there meanwhile.
 
 | tool | | answers |
 |---|---|---|
-| `kernel_boot` | r | the loader (`systemd-boot`, `grub` or `none`), the menu's entries, the kernels in `/boot`, the entry booted (systemd-boot) or the kernel image booted (GRUB), whether the fallback kernel is on the menu with its kernel in `/boot`, and the room free on `/boot` in KiB |
+| `kernel_boot` | r | the loader (`systemd-boot`, `grub` or `none`), the menu's entries, the kernels in `/boot`, the entry booted (systemd-boot) or the kernel image booted (GRUB), whether the fallback kernel is on the menu with its kernel in `/boot`, the room free on `/boot` in KiB, the microcode revision the CPU runs (`/proc/cpuinfo`) and, per `/boot/initramfs-*.img`, whether the image's first 64 KiB (the early uncompressed cpio) hold a path under `kernel/x86/microcode/` (`images_with_microcode`); an image that cannot be read is named with its error in `image_errors`, never counted as false |
 | `kernel_huge_pages` | r | the mode, defrag and shared-memory mode; each per-size control and what `inherit` resolves to; huge pages by kind from `/proc/meminfo` (MiB); the units holding the most file pages in huge folios (`memory.stat` `file_thp`) with their dirty and writeback bytes, khugepaged's collapses and the bytes their cgroup wrote (`io.stat`, the most any one device saw: a mirror and its members each count the same write) |
 
 ## Tests
 
 `go test ./...`: the tool over a stand-in tree holding the control node's own files of 2026-10-14; the
-manifest's shape (the default, the order, the unit and its sandbox, reload, restart and health); the kernel modules loaded at boot (`tun`) and the package and boot service that keep the running kernel's modules; the boot-entries script run with `sh` over stand-in roots (a systemd-boot entries directory, a GRUB menu, a hook that copies kernels to one fixed name): the entry from the booted command line, a menu generated again only when the kernels changed, no loader, no room, the taken-over hook; `kernel_boot` over the same roots; and the huge-pages script as the mesh
+manifest's shape (the default, the order, the unit and its sandbox, reload, restart and health); the kernel modules loaded at boot (`tun`) and the package and boot service that keep the running kernel's modules; the boot-entries script run with `sh` over stand-in roots (a systemd-boot entries directory, a GRUB menu, a hook that copies kernels to one fixed name): the entry from the booted command line, a menu generated again only when the kernels changed, no loader, no room, the taken-over hook; `kernel_boot` over the same roots; and the microcode drop-in sourced by bash, the initramfs script run with `sh` over a stand-in mkinitcpio (once, again on a changed drop-in, a failure recording nothing) and `kernel_boot`'s microcode answer (stand-in cpio images, one unreadable); and the huge-pages script as the mesh
 writes it, run with `sh` against a stand-in directory: it sets and reads back, keeps what it found once,
 rotates the journal once and not for `always` nor while the machine starts, goes straight to a new value on a
 reload without rewriting what it found, gives back what it found and then keeps nothing, refuses a value the kernel

modules/kernel/cmd/kernel-tools/boot.go

@@ -4,6 +4,8 @@ package main
 // whether the fallback kernel is on the menu (novox/hq ADR 0508 §9, issue 1841). Reads only.
 
 import (
+	"bytes"
+	"io"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -23,6 +25,50 @@ type BootState struct {
 	Booted          string   `json:"booted"`
 	FallbackPresent bool     `json:"fallback_present"`
 	BootFreeKiB     int64    `json:"boot_free_kib"`
+	// MicrocodeRevision is the revision the CPU runs, the first "microcode" line of /proc/cpuinfo ("" when it has none).
+	MicrocodeRevision string `json:"microcode_revision"`
+	// ImagesWithMicrocode is, per /boot/initramfs-*.img, whether the image's early uncompressed cpio (its first 64 KiB)
+	// holds a path under kernel/x86/microcode/ (novox/hq issue 1977).
+	ImagesWithMicrocode map[string]bool `json:"images_with_microcode"`
+	// ImageErrors names each image that could not be read and why: such an image is in no verdict above.
+	ImageErrors []ImageError `json:"image_errors"`
+}
+
+// ImageError is an initramfs image that could not be read.
+type ImageError struct {
+	Image string `json:"image"`
+	Error string `json:"error"`
+}
+
+var cpuMicrocode = regexp.MustCompile(`(?m)^microcode\s*:\s*(\S+)`)
+
+// microcode reads the revision the CPU runs and which initramfs images carry microcode.
+func (m *Machine) microcode(b *BootState) {
+	b.ImagesWithMicrocode = map[string]bool{}
+	b.ImageErrors = []ImageError{}
+	if raw, err := m.read("proc/cpuinfo"); err == nil {
+		if r := cpuMicrocode.FindStringSubmatch(raw); r != nil {
+			b.MicrocodeRevision = r[1]
+		}
+	}
+	images, _ := filepath.Glob(m.path("boot/initramfs-*.img"))
+	sort.Strings(images)
+	for _, img := range images {
+		name := filepath.Base(img)
+		f, err := os.Open(img)
+		if err != nil {
+			b.ImageErrors = append(b.ImageErrors, ImageError{name, err.Error()})
+			continue
+		}
+		head := make([]byte, 64*1024)
+		n, err := io.ReadFull(f, head)
+		f.Close()
+		if err != nil && err != io.ErrUnexpectedEOF && err != io.EOF {
+			b.ImageErrors = append(b.ImageErrors, ImageError{name, err.Error()})
+			continue
+		}
+		b.ImagesWithMicrocode[name] = bytes.Contains(head[:n], []byte("kernel/x86/microcode/"))
+	}
 }
 
 var grubKernel = regexp.MustCompile(`(?m)^\s*linux\s+(?:/boot)?/(vmlinuz-\S+)`)
@@ -33,6 +79,7 @@ var bootImage = regexp.MustCompile(`BOOT_IMAGE=(?:/boot)?/?(\S+)`)
 // systemd-boot, a grub.cfg without it GRUB.
 func (m *Machine) Boot() (*BootState, error) {
 	b := &BootState{Loader: "none", Entries: []string{}, Kernels: []string{}}
+	m.microcode(b)
 	files, _ := filepath.Glob(m.path("boot/vmlinuz-*"))
 	for _, f := range files {
 		b.Kernels = append(b.Kernels, filepath.Base(f))

modules/kernel/cmd/kernel-tools/main.go

@@ -51,7 +51,8 @@ func tools(m *Machine) []stdio.Tool {
 			Description: "How this machine boots and whether the fallback kernel is on its menu (novox/hq ADR 0508 §9): the loader that booted it " +
 				"(systemd-boot, read from the EFI variable it sets, grub, or none), the menu's entries, the kernels in /boot, the entry " +
 				"the machine booted (systemd-boot) or the kernel image it booted (grub), whether the fallback kernel linux-lts is on " +
-				"the menu with its kernel in /boot, and the room free on /boot in KiB (the fallback kernel needs about 72 MB). " +
+				"the menu with its kernel in /boot, and the room free on /boot in KiB (the fallback kernel needs about 72 MB), the microcode revision the CPU runs " +
+				"(/proc/cpuinfo) and, per /boot/initramfs-*.img, whether its early cpio carries microcode (images_with_microcode; an unreadable image is named in image_errors) (novox/hq issue 1977). " +
 				"Replaces ls /boot, bootctl list, reading grub.cfg and df /boot. (r)",
 			Input: schema(map[string]any{}),
 			Run:   func(args map[string]any) (any, error) { return m.Boot() },

modules/kernel/cmd/kernel-tools/manifest_test.go

@@ -24,7 +24,7 @@ func TestTheDefaultIsMadviseAndTheUnitFollowsTheSetting(t *testing.T) {
 	for _, r := range m.Resources {
 		ids = append(ids, r["id"].(string))
 	}
-	if strings.Join(ids, " ") != "state huge-pages unit apply boot-entries boot-unit boot-hook boot-apply linux-lts linux-lts-headers modules-load modules-keep modules-cleanup" {
+	if strings.Join(ids, " ") != "state huge-pages unit apply boot-entries boot-unit boot-hook boot-apply linux-lts linux-lts-headers modules-load modules-keep modules-cleanup amd-ucode intel-ucode microcode-hook initramfs initramfs-unit initramfs-apply" {
 		t.Fatalf("order: %v", ids)
 	}
 	script := m.resource(t, "huge-pages")

modules/kernel/cmd/kernel-tools/microcode_test.go

@@ -0,0 +1,190 @@
+package main
+
+// Microcode in every initramfs (novox/hq issue 1977, lead answers L1-L4): the manifest, the drop-in sourced by bash,
+// the initramfs script run with sh over stand-in files and a stand-in mkinitcpio, and kernel_boot's answer.
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// 1977/AC1
+func TestAC1TheManifestDeclaresTheMicrocodePackagesDropInScriptAndService(t *testing.T) {
+	m := manifest(t)
+	var ids []string
+	for _, r := range m.Resources {
+		ids = append(ids, r["id"].(string))
+	}
+	if !strings.HasSuffix(strings.Join(ids, " "), "modules-cleanup amd-ucode intel-ucode microcode-hook initramfs initramfs-unit initramfs-apply") {
+		t.Fatalf("order: %v", ids)
+	}
+	for id, pkg := range map[string]string{"amd-ucode": "amd-ucode", "intel-ucode": "intel-ucode"} {
+		if r := m.resource(t, id); r["type"] != "package" || r["package"] != pkg {
+			t.Fatalf("%s: %v", id, r)
+		}
+	}
+	if r := m.resource(t, "microcode-hook"); r["path"] != "/etc/mkinitcpio.conf.d/mesh-microcode.conf" {
+		t.Fatalf("drop-in: %v", r)
+	}
+	if r := m.resource(t, "initramfs"); r["path"] != "${dir:state}/initramfs" || r["mode"] != "0755" || r["trusted"] != true {
+		t.Fatalf("script: %v", r)
+	}
+	if r := m.resource(t, "initramfs-unit"); r["path"] != "/etc/systemd/system/mesh-kernel-initramfs.service" {
+		t.Fatalf("unit: %v", r)
+	}
+	a := m.resource(t, "initramfs-apply")
+	on := a["restart-on"].([]any)
+	if a["unit"] != "mesh-kernel-initramfs.service" || a["state"] != "running" || a["boot"] != "enabled" ||
+		len(on) != 3 || on[0] != "initramfs-unit" || on[1] != "initramfs" || on[2] != "microcode-hook" {
+		t.Fatalf("service: %v", a)
+	}
+}
+
+// 1977/AC2
+func TestAC2TheDropInAddsMicrocodeToHooksOnce(t *testing.T) {
+	drop := filepath.Join(t.TempDir(), "mesh-microcode.conf")
+	write(t, drop, manifest(t).resource(t, "microcode-hook").text(t), 0o644)
+	for _, c := range []struct{ hooks, want string }{
+		{"base udev autodetect modconf block filesystems keyboard fsck", "base udev autodetect modconf block filesystems keyboard fsck microcode"},
+		{"base udev autodetect microcode block", "base udev autodetect microcode block"},
+	} {
+		out, err := exec.Command("bash", "-c", "HOOKS=("+c.hooks+"); . "+drop+"; echo \"${HOOKS[*]}\"").CombinedOutput()
+		if err != nil || strings.TrimSpace(string(out)) != c.want {
+			t.Errorf("%q: %v %q", c.hooks, err, out)
+		}
+	}
+}
+
+type initBed struct{ script, dropin, state, runs, bin, presets, boot string }
+
+func newInitBed(t *testing.T, mkinitcpioExit string) initBed {
+	t.Helper()
+	dir := t.TempDir()
+	b := initBed{script: filepath.Join(dir, "initramfs"), dropin: filepath.Join(dir, "mesh-microcode.conf"), state: filepath.Join(dir, "state"),
+		runs: filepath.Join(dir, "runs"), bin: filepath.Join(dir, "bin"), presets: filepath.Join(dir, "presets"), boot: filepath.Join(dir, "boot")}
+	for _, d := range []string{b.state, b.bin, b.presets, b.boot} {
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	content := strings.ReplaceAll(manifest(t).resource(t, "initramfs").text(t), "${dir:state}", b.state)
+	if strings.Contains(content, "${") {
+		t.Fatal("a substitution is left in the script")
+	}
+	write(t, b.script, content, 0o755)
+	write(t, b.dropin, "HOOKS+=(microcode)\n", 0o644)
+	// the stand-in mkinitcpio writes an image whose early archive holds microcode.
+	b.mkinitcpio(t, "kernel/x86/microcode/AuthenticAMD.bin", mkinitcpioExit)
+	return b
+}
+
+func (b initBed) mkinitcpio(t *testing.T, early, exit string) {
+	write(t, filepath.Join(b.bin, "mkinitcpio"), "#!/bin/sh\necho \"$@\" >>"+b.runs+"\nprintf '070701%s\\0' "+early+" >"+b.boot+"/initramfs-linux.img\nexit "+exit+"\n", 0o755)
+}
+
+func (b initBed) run(t *testing.T) (string, error) {
+	cmd := exec.Command("sh", b.script, "apply", b.dropin, b.state, b.presets, b.boot)
+	cmd.Env = append(os.Environ(), "PATH="+b.bin+string(os.PathListSeparator)+os.Getenv("PATH"))
+	out, err := cmd.CombinedOutput()
+	return string(out), err
+}
+
+func (b initBed) builds(t *testing.T) string {
+	raw, _ := os.ReadFile(b.runs)
+	return string(raw)
+}
+
+// 1977/AC3
+func TestAC3TheImagesAreBuiltOnceAndAgainWhenTheDropInChanges(t *testing.T) {
+	b := newInitBed(t, "0")
+	if out, err := b.run(t); err != nil || b.builds(t) != "-P\n" {
+		t.Fatalf("first: %v %s %q", err, out, b.builds(t))
+	}
+	if raw, _ := os.ReadFile(filepath.Join(b.state, "initramfs-built")); string(raw) != "HOOKS+=(microcode)\n" {
+		t.Fatalf("recorded: %q", raw)
+	}
+	if out, err := b.run(t); err != nil || !strings.Contains(out, "as it was") || b.builds(t) != "-P\n" {
+		t.Fatalf("again: %v %s %q", err, out, b.builds(t))
+	}
+	write(t, b.dropin, "HOOKS+=(microcode)\n# new\n", 0o644)
+	if _, err := b.run(t); err != nil || b.builds(t) != "-P\n-P\n" {
+		t.Fatalf("changed: %v %q", err, b.builds(t))
+	}
+}
+
+// 1977/AC4
+func TestAC4AFailedMkinitcpioFailsTheUnitAndRecordsNothing(t *testing.T) {
+	b := newInitBed(t, "1")
+	out, err := b.run(t)
+	if err == nil || !strings.Contains(out, "mkinitcpio failed") {
+		t.Fatalf("%v %s", err, out)
+	}
+	if _, err := os.Stat(filepath.Join(b.state, "initramfs-built")); !os.IsNotExist(err) {
+		t.Fatalf("recorded after a failure: %v", err)
+	}
+}
+
+// 1977/AC5
+func TestAC5KernelBootNamesTheRunningMicrocodeAndWhichImagesCarryIt(t *testing.T) {
+	root := t.TempDir()
+	put(t, root, "proc/cpuinfo", "processor\t: 0\nmicrocode\t: 0x0a201016\nmodel name\t: x\n")
+	// a stand-in early cpio: a name field, then padding, as the first member of an initramfs.
+	put(t, root, "boot/initramfs-linux.img", "070701000000kernel/x86/microcode/AuthenticAMD.bin\x00\x00"+strings.Repeat("z", 100))
+	put(t, root, "boot/initramfs-linux-lts.img", "070701000000early/other.bin\x00"+strings.Repeat("z", 100))
+	got := bootOf(t, root)
+	if got.MicrocodeRevision != "0x0a201016" || len(got.ImagesWithMicrocode) != 2 ||
+		!got.ImagesWithMicrocode["initramfs-linux.img"] || got.ImagesWithMicrocode["initramfs-linux-lts.img"] || len(got.ImageErrors) != 0 {
+		t.Fatalf("%+v", got)
+	}
+	if os.Getuid() == 0 {
+		t.Skip("root reads an unreadable file")
+	}
+	bad := filepath.Join(root, "boot/initramfs-linux-fallback.img")
+	put(t, root, "boot/initramfs-linux-fallback.img", "x")
+	if err := os.Chmod(bad, 0); err != nil {
+		t.Fatal(err)
+	}
+	got = bootOf(t, root)
+	if _, in := got.ImagesWithMicrocode["initramfs-linux-fallback.img"]; in || len(got.ImageErrors) != 1 ||
+		got.ImageErrors[0].Image != "initramfs-linux-fallback.img" || got.ImageErrors[0].Error == "" {
+		t.Fatalf("unreadable: %+v", got)
+	}
+}
+
+// 1977/AC7
+func TestAC7ADefaultConfigPresetIsTakenOverAndAnotherIsLeftAndNamed(t *testing.T) {
+	b := newInitBed(t, "0")
+	preset := "ALL_kver=\"/boot/vmlinuz-linux\"\nALL_config=\"/etc/mkinitcpio.conf\"\nPRESETS=('default')\n"
+	write(t, filepath.Join(b.presets, "linux.preset"), preset, 0o644)
+	other := "ALL_config=\"/etc/other.conf\"\nPRESETS=('default')\n"
+	write(t, filepath.Join(b.presets, "linux-lts.preset"), other, 0o644)
+	out, err := b.run(t)
+	if err != nil {
+		t.Fatalf("%v %s", err, out)
+	}
+	if got, _ := os.ReadFile(filepath.Join(b.presets, "linux.preset")); string(got) != "ALL_kver=\"/boot/vmlinuz-linux\"\nPRESETS=('default')\n" {
+		t.Fatalf("preset: %q", got)
+	}
+	if got, _ := os.ReadFile(filepath.Join(b.state, "taken-over", "linux.preset")); string(got) != preset {
+		t.Fatalf("copy: %q", got)
+	}
+	if got, _ := os.ReadFile(filepath.Join(b.presets, "linux-lts.preset")); string(got) != other || !strings.Contains(out, "linux-lts.preset sets ALL_config=\"/etc/other.conf\"") {
+		t.Fatalf("other: %q %s", got, out)
+	}
+}
+
+// 1977/AC8
+func TestAC8AnImageWithoutMicrocodeFailsTheUnitNamesItAndRecordsNothing(t *testing.T) {
+	b := newInitBed(t, "0")
+	b.mkinitcpio(t, "early/other.bin", "0")
+	out, err := b.run(t)
+	if err == nil || !strings.Contains(out, "initramfs-linux.img") {
+		t.Fatalf("%v %s", err, out)
+	}
+	if _, err := os.Stat(filepath.Join(b.state, "initramfs-built")); !os.IsNotExist(err) {
+		t.Fatalf("recorded: %v", err)
+	}
+}

modules/kernel/files/initramfs.sh

@@ -0,0 +1,71 @@
+#!/bin/sh
+# The initramfs images as the mesh builds them (module kernel, novox/hq issue 1977). Run by
+# mesh-kernel-initramfs.service:
+#
+#   initramfs apply [<the microcode drop-in> [<this module's state> [<preset directory> [<boot directory>]]]]
+#
+# `apply` builds every image again (mkinitcpio -P) when the drop-in differs from the one the images were last built
+# with, kept in the state as `initramfs-built`, and records the drop-in only after mkinitcpio succeeded. Later
+# kernel upgrades build the images through the distribution's own hook, with the drop-in in place.
+#
+# A preset that names the default configuration (ALL_config="/etc/mkinitcpio.conf") makes mkinitcpio pass -c and skip
+# mkinitcpio.conf.d, so the drop-in is never read: before building, that line is taken out of the preset, a copy of
+# the preset kept in the state's taken-over directory (novox/hq ADR 0508 §10's way with a file the mesh did not
+# write); any other ALL_config is left and named. After building, every image must hold microcode in its first
+# 64 KiB (the early uncompressed archive), else the unit fails and records nothing. The arguments are only for the
+# module's tests.
+set -eu
+
+dropin=/etc/mkinitcpio.conf.d/mesh-microcode.conf
+state='${dir:state}'
+[ $# -ge 2 ] && dropin=$2
+[ $# -ge 3 ] && state=$3
+presets=/etc/mkinitcpio.d
+boot=/boot
+[ $# -ge 4 ] && presets=$4
+[ $# -ge 5 ] && boot=$5
+
+[ $# -ge 1 ] && [ "$1" = apply ] || {
+	echo "usage: initramfs apply [<drop-in> [<state directory>]]" >&2
+	exit 2
+}
+[ -f "$dropin" ] || {
+	echo "initramfs: $dropin is not there, so the images cannot be built with the microcode hook" >&2
+	exit 1
+}
+if [ -f "$state/initramfs-built" ] && cmp -s "$dropin" "$state/initramfs-built"; then
+	echo "initramfs: the images were built with this drop-in, as it was"
+	exit 0
+fi
+for preset in "$presets"/*.preset; do
+	[ -f "$preset" ] || continue
+	if grep -qx 'ALL_config="/etc/mkinitcpio.conf"' "$preset"; then
+		mkdir -p "$state/taken-over"
+		cp "$preset" "$state/taken-over/$(basename "$preset")"
+		grep -vx 'ALL_config="/etc/mkinitcpio.conf"' "$preset" >"$preset.new" || true
+		cat "$preset.new" >"$preset"
+		rm -f "$preset.new"
+		echo "initramfs: $preset named the default configuration, which skips mkinitcpio.conf.d; that line is taken out, a copy is in $state/taken-over"
+	elif grep -q '^ALL_config=' "$preset"; then
+		echo "initramfs: $preset sets $(grep '^ALL_config=' "$preset" | head -n 1), so the microcode drop-in may not be read; left as it is"
+	fi
+done
+if ! mkinitcpio -P; then
+	echo "initramfs: mkinitcpio failed; nothing recorded, the next start tries again" >&2
+	exit 1
+fi
+missing=
+for img in "$boot"/initramfs-*.img; do
+	[ -e "$img" ] || continue
+	if ! head -c 65536 "$img" >"$state/image-head.tmp" || ! grep -aq 'kernel/x86/microcode/' "$state/image-head.tmp"; then
+		missing="$missing $(basename "$img")"
+	fi
+done
+rm -f "$state/image-head.tmp"
+if [ -n "$missing" ]; then
+	echo "initramfs: mkinitcpio ran, but no microcode is in the early archive of:$missing; nothing recorded" >&2
+	exit 1
+fi
+cp "$dropin" "$state/initramfs-built.new"
+mv "$state/initramfs-built.new" "$state/initramfs-built"
+echo "initramfs: the images are built with the microcode drop-in"

modules/kernel/files/mesh-kernel-initramfs.service

@@ -0,0 +1,22 @@
+[Unit]
+Description=The initramfs images with the CPU's current microcode
+# Module kernel, novox/hq issue 1977. Starting this unit builds the images again when the microcode drop-in
+# changed since they were last built; a failed mkinitcpio fails the unit. The microcode packages are declared
+# before this unit.
+After=local-fs.target
+Wants=local-fs.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=${dir:state}/initramfs apply
+# It writes the boot partition, the presets and its own state; mkinitcpio keeps its work in a private /tmp.
+ProtectSystem=strict
+ReadWritePaths=/boot /etc/mkinitcpio.d ${dir:state}
+PrivateTmp=yes
+ProtectHome=yes
+PrivateNetwork=yes
+NoNewPrivileges=yes
+
+[Install]
+WantedBy=multi-user.target

modules/kernel/files/mesh-microcode.conf

@@ -0,0 +1,8 @@
+# Module kernel, novox/hq issue 1977. mkinitcpio reads this after /etc/mkinitcpio.conf: it adds the microcode
+# hook, which puts the CPU's current microcode (amd-ucode, intel-ucode) at the front of every initramfs, so
+# every boot entry loads it, the default one too. HOOKS that name it already are left as they are.
+# Written by the mesh; change the module.
+case "$(declare -p HOOKS)" in
+*'"microcode"'*) ;;
+*) HOOKS+=(microcode) ;;
+esac

modules/kernel/module.json

@@ -119,6 +119,53 @@
       "unit": "linux-modules-cleanup.service",
       "state": "stopped",
       "boot": "enabled"
+    },
+    {
+      "id": "amd-ucode",
+      "type": "package",
+      "package": "amd-ucode"
+    },
+    {
+      "id": "intel-ucode",
+      "type": "package",
+      "package": "intel-ucode"
+    },
+    {
+      "id": "microcode-hook",
+      "type": "file",
+      "path": "/etc/mkinitcpio.conf.d/mesh-microcode.conf",
+      "mode": "0644",
+      "template": "files/mesh-microcode.conf"
+    },
+    {
+      "id": "initramfs",
+      "type": "file",
+      "path": "${dir:state}/initramfs",
+      "mode": "0755",
+      "trusted": true,
+      "template": "files/initramfs.sh"
+    },
+    {
+      "id": "initramfs-unit",
+      "type": "file",
+      "path": "/etc/systemd/system/mesh-kernel-initramfs.service",
+      "mode": "0644",
+      "template": "files/mesh-kernel-initramfs.service"
+    },
+    {
+      "id": "initramfs-apply",
+      "type": "service",
+      "unit": "mesh-kernel-initramfs.service",
+      "state": "running",
+      "boot": "enabled",
+      "restart-on": [
+        "initramfs-unit",
+        "initramfs",
+        "microcode-hook"
+      ],
+      "health": {
+        "kind": "unit"
+      }
     }
   ],
   "build": {