To modify the CPUID emulation code in KVM to report back a fictitious processor ID string when callers request CPUID leaf 0x0
The following procedure describes the steps followed to develop and test the kernel module necessary for this assignment:
- Install packages necessary to compile the linux kernel from source:
sudo aptget install git buildessential kernelpackage fakeroot libncurses5dev libssldev ccache
- Clone the kernel sources from the master linux git repository:
git clone https://github.com/torvalds/linux.git
This clones the linux kernel sources to a directory named "linux".
- Change to the cloned directory:
cd linux
- Generate the kernel configuration file ".config" using the following command. If this command fails with any missing packages, install them using sudo apt-get install
make menuconfig
- Compile and install the kernel and its modules and also copy the kernel and the .config file to the /boot folder and to generate the system.map file using the following commands: To know the number of processing units, in my case it was 1 core.
nproc Specify the number of cores in -j option in the following command to speed up the process. sudo make -j 1 && sudo make modules_install -j 1 && sudo make install -j 1
- Run the following command to check the kernel version
uname r
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Reboot and select the newly built kernel in the boot loader config (if not already).
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Verify that we are running the newly built kernel using the following command:
uname r For example, in the VM used for this assignment the output of "uname -r" before and after installing the new kernel are shown below:
Before reboot:
uname r 4.13.0.36-generic
After reboot:
uname r 4.16.0-rc4+ Note: Once the above kernel is running, testing any new changes made to the KVM sources would just require rebuilding (and re-inserting) the kvm and kvm-intel modules, which is accomplished using the following command:
sudo make modules SUBDIRS=arch/x86/kvm/ Module development The changes to KVM, necessary to implement the assignment functionality required modification to the kvm_emulate_cpuid in the following file: arch/x86/kvm/cpuid.c
- Build only the kvm modules using the following command inside the linux directory:
sudo make modules SUBDIRS=arch/x86/kvm/
- Load and unload the kvm kernel module (kvm.ko) and kvm-intel module (kvm-intel.ko) using the following commands:
sudo rmmod arch/x86/kvm/kvm-intel.ko sudo rmmod arch/x86/kvm/kvm.ko
sudo insmod arch/x86/kvm/kvm.ko sudo insmod arch/x86/kvm/kvm-intel.ko
Now to test this change to CPUID.c create a VM (let’s call it VM-1).
- Use the following command to install KVM and supporting packages.
sudo apt-get install qemu-kvm libvirt-bin bridge-utils virt-manager
- Verify KVM Installation using the following command. You should see an empty list of virtual machines. This indicates that everything is working correctly.
virsh -c qemu:///system list
- Install Virt-Manager
sudo apt-get install virt-manager
- Install CPUID by using the following command
sudo apt-get install cupid
CPUID gives a whole list of CPUID features of which the first one is the vendor string.
- Compile and run the test file provided inside VM-1.
Run the program without any input supplied.
Run the program again with a user input.
