1. copy the /boot/config-xxx from guest

   scp root@guest_ip:/boot/config-3.13-xxx .config

2. change your guest ip and modules path in config.sh

3. In linux src directory, yes "" | make oldconfig

4. In linux src directory, make menuconfig, in virtualization, mark KVM and intel part to * (builtin), In Kernel Hacking - Compile time checks and options, turn on the Provide GDB scripts for kernel debugging, then save the config.

   In Device Drivers > Network device support > Ethernet driver support,

<*>     RealTek RTL-8139 C+ PCI Fast Ethernet Adapter support
<*>     RealTek RTL-8129/8130/8139 PCI Fast Ethernet Adapter support

5. bash build.sh to compile
6. bash update-guest.sh to install new kernel for guest os

In guest os, modify /etc/ssh/sshd_config to allow ssh as root

#PermitRootLogin without-password
StrictModes yes
PermitRootLogin yes
PasswordAuthentication yes

then setup root password with sudo passwd root then sudo service ssh restart then use setup-sshkey.sh to setup ssh key access with guest vm.

Run sudo virsh edit guest0 to edit the xml spec.

# Modify this:
<domain type='kvm'>
# To look like this:
<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <qemu:commandline>
    <qemu:arg value='-s'/> # add -S to wait for gdb before booting
  </qemu:commandline>

To enable nested virtualization vmx feature, sudo virsh edit guest0 to modify the cpu attribute to,

  <cpu mode='host-model' check='partial'>
    <model fallback='allow'>Haswell-noTSX-IBRS</model>
  </cpu>

  or add <feature policy='require' name='vmx'/> inside <cpu> section

add the following line to ~/.gdbinit to allow loading helper files:

set auto-load safe-path /

modify /etc/default/grub.

#GRUB_HIDDEN_TIMEOUT=-1
#GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=-1
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nokaslr"
GRUB_CMDLINE_LINUX="console=ttyS0,115200n8"

add nokaslr to cmdline_linux_default (for gdb breakpoint to work) to /etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nokaslr"

Then sudo update-grub.

start the guest, and then navigate to the linux source directory in host,

gdb vmlinux

In gdb:

(gdb) lx-symbols
(gdb) target remote :1234
(gdb) hb vmx_init
(gdb) c

hb = hardware breakpoint, (normal breakpoint not working).

then you can play with gdb, see https://01.org/linuxgraphics/gfx-docs/drm/dev-tools/gdb-kernel-debugging.html for info on helper commands like lx-symbols.