Amazon Proposes Pkernfs For Better Handling Hypervisor Live Updates

Stemming from work done at Amazon Web Services (AWS) for better handling hypervisor live updates, a "request for comments" patch series was sent out on the Linux kernel mailing list for Pkernfs. The Pkernfs proposal was first detailed publicly by AWS last year and is for persisting guest memory and kernel/device state safely across Kexec.

James Gowans with Amazon explained of Pkernfs in yesterday's RFC proposal:

"This RFC is to solicit feedback on the approach of implementing support for live update via an in-memory filesystem responsible for storing all live update state as files in the filesystem.

Hypervisor live update is a mechanism to support updating a hypervisor via kexec in a way that has limited impact to running virtual machines. This is done by pausing/serialising running VMs, kexec-ing into a new kernel, starting new VMM processes and then deserialising/resuming the VMs so that they continue running from where they were. Virtual machines can have PCI devices passed through and in order to support live update it’s necessary to persist the IOMMU page tables so that the devices can continue to do DMA to guest RAM during kexec."

Last November at the Linux Plumbers Conference (LPC 2023) is where the work on Pkernfs was originally detailed. That LPC presentation on Pkernfs can be found at LPC.events for those interested in more background and motivation on this project.

Pkernfs is just around one thousand lines of new code and is now out for review on the Linux kernel mailing list.