fix: disable Kexec Handover to free up ~128MiB of RAM (#2472)

* fix: disable Kexec Handover to free up ~128MiB of RAM

Required for KUBE-1370.

kho reserves memory to be handed over to the kexec'ed kernel; on memory
constrained instances this is a significant amount of memory. Disable
kho since we don't use kexec to reboot anyway.

* fix: use the .cfg extension for grub config

---------

Co-authored-by: Nicola Ferraro <ni.ferraro@gmail.com>

Author: lowjoel

ansible/handlers/main.yml

@@ -0,0 +1,2 @@
+- name: Regenerate grub configuration
+  ansible.builtin.import_tasks: update-grub.yml

ansible/handlers/update-grub.yml

@@ -0,0 +1,4 @@
+- name: Regenerate grub configuration
+  ansible.builtin.command:
+    cmd: 'update-grub'
+  changed_when: true

ansible/playbook.yml

@@ -205,3 +205,7 @@
       when: stage2 and not qemu
       become: yes
       import_tasks: tasks/stage2/setup-swap.yml
+
+  handlers:
+    - name: Import handlers
+      import_tasks: handlers/main.yml

ansible/tasks/setup-system.yml

@@ -109,6 +109,16 @@
         owner: 'root'
         group: 'root'
 
+    - name: Disable kexec handover # Saves ~128 MiB of RAM on a nano.
+      ansible.builtin.copy:
+        content:
+          GRUB_CMDLINE_LINUX_DEFAULT="${GRUB_CMDLINE_LINUX_DEFAULT} kho=off"
+        dest: /etc/default/grub.d/51-disable-kho.cfg
+        owner: root
+        group: root
+      notify:
+        - Regenerate grub configuration
+
 - name: Disable algif_aead module autoload for Copy Fail mitigation
   ansible.builtin.copy:
     content: |