Xen in Linux 3.2, 3.3 and Beyond

Linux 3.2
Linux 3.2 was released on Jan 4th and compared to earlier kernel releases, this one was very focused on fixing bugs reported by the community.

Thank you!!

Issues that caused lots of bug reports were:

  • The xen-platform-pci module (used for HVM guest to enable PV drivers) was frequently not included in the installer (that is now fixed by making it built in the kernel and fixing the installer builders).
  • ‘xl list’ vs ‘xm list’ discrepancy: this was caused by the guest not having the memory in the “right” sections.
  • Others were related to issues found with Amazon EC2, and bug fixes from Linux distributions (Debian, Canonical, Fedora, Red Hat, Citrix  and Oracle).
  • We also fixed boot issues for Dell machines.

We are all quite grateful for community reporting these issues! For reported issues, it might take some time to find the root cause. We do want to get them all fixed and hope that you will be patient with us.

On the “feature” side we

  • cleaned the code
  • added support for big machines with more than 256 PCI devices
  • added kexec support for PVonHVM (which sadly broke Amazon EC2, so we are going to redo them)
  • initial work laid out for HVM device driver domains
  • added features to support discard (TRIM or UNMAP) in the block layer along with the emulation of barriers

Linux 3.3
The Linux 3.3 merge window opened a week ago, and we had a similar pattern of patches: documentation cleanups (Thanks to the Document Day), security fixes, fixes in the drivers, driver cleanups, and fixes in the config options.

Feature wise a new driver for doing ioctl to the hypervisor was introduced, more infrastructure changes to improve the netback driver (grant table and skb changes), and making the netback driver be able to work in an HVM guest (the blkback is coming next). The graphic side introduced an DMA type pool code in the TTM backend (used by both radeon and nouveau to fetch/put all of the pages used by the adapter) so that it can work faster and also properly under Xen (the major issues were with 32-bit cards). i915 does not use TTM so it did not need this.

Linux 3.4 and beyond
So what is next? The top things we want to accomplish this year is to:

  • Make ACPI power management work with Xen.
  • Make netback work much much better than it does now!
  • Allow backends and xenstore to run in guests, allowing separate device driver domains
  • Improve the documentation
  • Fix more bugs!

There are other items on this list too, but these ones are the most important right now.