Abhijeet Dev

While working on virtualisation of custom services, I came across ivshmem module in kvm that I am now using to have interrupts and shared memory between host and multiple guests. Setting it up is easy, but available documentation is outdated.

Configuration
Host: Ubuntu 11.10, installed qemu-kvm
Guest: Gentoo, for minimal configuration and maximum customisability

Making it work

1. Download and compile ivshmem support code from nahanni’s gitorious repo  on host and guest(s):
   git clone https://git.gitorious.org/nahanni/guest-code.git
2. [Host] Go to ivshmem_server folder in downloaded code, build and run the following:
   ./ivshmem_server -m 512 -s nahanni -p /tmp/nahanni
3. [Host] Run guest vm(s) using the following command line (or any other arguments):
   kvm -boot d -hda vhost-gentoo.raw -cpu core2duo -m 1G -chardev socket,path=/tmp/nahanni,id=nahanni -device ivshmem,chardev=nahanni,size=512m,ioeventfd=on,vectors=8
4. [Guest] Go to kernel_module/standard folder in downloaded code, build and run
   insmod kvm_ivshmem.ko
5. Check the kernel messages, make sure you see ‘MSI-X enabled’. If there is any error, fix the error first.
   dmesg | tail
6. Check major number allocated to the char device created:
   cat /proc/devices | grep kvm_ivshmem
7. Use the major number above – it’s ’250′ for my sequence of actions on my configured VM.
   mknod --mode=666 /dev/ivshmem c 250 0
8. If you have multiple ivshmem devices serving different purposes
   # for each ivshmem device
   mknod --mode=666 /dev/ivshmem<n> c <n>
9. It works now! Try the test code in tests folder in downloaded support code.

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