The document discusses the status and strategy for updating the Linux kernel to support para-virtualized (PV) operations. It describes the current state of the PV-ops kernel, which allows one kernel to run on different virtualization platforms like Xen, KVM, and VMware. The primary goals are refactoring code for upstream submission, stabilizing existing branches, and keeping branches rebased against newer kernels. Several key components like SWIOTLB and PCI frontend drivers are being refactored and tested for upstream inclusion.

1. PV-ops Linux kernel update
Jeremy Fitzhardinge &
Konrad Rzeszutek Wilk
Xen Summit at AMD 1
April 28-29, 2010

2. Agenda
 Primer on para-virtualized operations
 Pros & cons of PV-ops vs XenLinux
 Upstream strategy
 Current status
 Outstanding issues
 Explanation of GIT branches
Xen Summit at AMD 2
April 28-29, 2010

3. Primer (1/2)
 http://wiki.xensource.com/xenwiki/XenParavirtOps
 Linux kernel can be booted on:
 Baremetal
 Hardware assisted virtualization (HVM)
 Para-virtualization (PV)
 PV requires modifications in the Linux kernel.
 In the past, two variants of the kernel:
 baremetal (which can also do HVM) - kernel
 Para-virtualized kernel (kernel-xen)
Xen Summit at AMD 3
April 28-29, 2010

4. Primer (2/2)
 Para-Virtualization Operations (PV-ops):
 Detects if running in HVM, VMWare, Xen, KVM
 Patches all low-level privileged operations (memory
updates, spinlocks, etc) with appropiate
virtualization aware calls.
 End-result:
 One kernel to boot under different X86 platforms.
 Lower QA
 No #ifdef CONFIG_XEN (frowned on by everybody)
Xen Summit at AMD 4
April 28-29, 2010

5. PV-ops & XenLinux (1/2)
 XenLinux (2.6.18, 2.6.27, 2.6.31, 2.6.32):
 Runs only under Xen.
 Has much big breadth of Xen back/front drivers (PV scsi, PV
usb, Netchannel 2) and can work with proprietary drivers:
nvidia, acronis snapapi, etc.
 Super stable (2.6.18, 2.6.27)
 Not upstreamable
 Performance
 PV-ops (2.6.31, 2.6.32):
 Lower testing requirements (one kernel)
 Share code base with X86 common code function.
Xen Summit at AMD 5
 New development April 28-29, 2010

6. PV-ops & XenLinux (2/2)
 http://wiki.xensource.com/xenwiki/XenDom0Kernels
 XenLinux distros:
 RHEL5, OVM
 OpenSUSE 11/SLES11
 Debian (lenny, etch)
 XenSource (XCP)
 PV-ops distributions:
 Fedora Core (unofficial)
 http://myoung.fedorapeople.org/dom0
 Debian squeeze
 http://packages.debian.org/xen-linux-system-2.6.32
Xen Summit at AMD 6
April 28-29, 2010

7. Upstream strategy (1/3)
 Three code ”camps”:
 DomU (unprivileged PV guests). Mostly frontend
drivers and Linux has many already in: Network,
Disk, Framebuffer, Keyboard, and Console.
Missing: PCI frontend.
 Dom0 (privileged PV guest). Main guest handling
PCI devices, ACPI, IOAPIC, KMS, XServer. PAT,
MTRR, MSI, etc. None are upstream.
 Shared between baremetal, DomU and Dom0. For
example: Software IOMMU (SWIOTLB).
Xen Summit at AMD 7
April 28-29, 2010

8. Upstream strategy (2/3)
 Jeremy git branch has DomU, Dom0 and
shared code.
 Konrad git has DomU and shared code.
 Strategy is to seperate the functionality patches
in separate branches so they can be submitted
upstream as whole ”functional” pieces. For
example: xen/core, xen/dom0/apic
 But many are built on top of each other. For
example: XenPCI front requires Xen-SWIOTLB.
Xen Summit at AMD 8
April 28-29, 2010

9. Upstream strategy (3/3)
 Three-pronged strategy:
 Constantly refactor code for upstream submission.
 Stabilize existing Dom0 branch so that distros can
pick it up (Debian, Fedora, Qubes-OS, XenServer)
 Rebase existing branches against newer kernels to
keep up
Xen Summit at AMD 9
April 28-29, 2010

10. Status (1/3) - refactoring
 SWIOTLB changes submitted upstream
 Xen-SWIOTLB – waiting
 Xen PCI and Xen PCI frontend– waiting
 Has been tested by community members with success
 pv/merge-2.6.33, pv/merge.2.6.34-rc3
 PV on HVM – work in progress
 PAT – being tested
 IO APIC/ACPI – researching solution
 MSI – researching solution
Xen Summit at AMD 10
April 28-29, 2010

11. Status (2/3) - stabilizing
 xen/stable-2.6.[31|32|33].x:
 Community providing many reports
 And patches as well
 And Wiki writeups!
 Tracking mainline long-term stable-2.6.[31|32|33] while
incorporating Xen fixes
 xen/next is the development branch:
 Xen bug-fixes only
 New ideas on solving problems (ACPI GSI IRQ 20)
 What is stable trickles down to xen/stable-2.6.[31|32|
33].x Xen Summit at AMD 11
April 28-29, 2010

12. Status (3/3) - rebasing
 Konrad's pv/pcifront-2.6.3[X] and swiotlb-0.Y
rebased to keep up with upstream tree.
 Unprivileged PV (DomU) and X86 shared code
 git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git
 Jeremy's xen/stable-2.6.3[X]:
 privileged & unprivileged PV & X86 shared code.
 git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git
 .34 still work in progress
Xen Summit at AMD 12
April 28-29, 2010

13. Outstanding issues
 Desktop video card (Nvidia, ATI, Intel)
 http://wiki.xensource.com/xenwiki/XenPVOPSDRM
 DRM
 X Server
 Kernel Mode Setting
 Direct Rendering Manager/TTM
 Network between DomU and Dom0
Xen Summit at AMD 13
April 28-29, 2010

14. Thanks
 Thanks to Xen community who have taken the
time and effort to work with and on the PV-ops
kernel.
Xen Summit at AMD 14
April 28-29, 2010

15. Jeremy's GIT branches
 git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git
 xen/next – base Xen developments against 2.6.32, no
kernel updates or fixes
 xen/stable-2.6.[31|32|33] – tracking mainline long-term
stable-2.6.[31|32|33] while incorporating Xen updates
 xen/core – PV and shared code. PTE, IRQ
 xen/dev-evtchn – PV and shared code. Events
 xen/dom0/core – privileged PV (dom0) code. MTRR,
PAT, HPET, etc
 xen/dom0/msi – privileged PV (dom0) MSI code
 xen/backend/core – Xen backend base
Xen Summit at AMD 15
April 28-29, 2010

16. Konrad's GIT branches
 git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git
 pv/pcifront-2.6.[32|33|34] – Xen PCI & Xen PCI
frontend driver.
 xen-swiotlb-0.7 – latest Xen-SWIOTLB code
 pv/merge.2.6.[32|33|34] – both branches above
combined
Xen Summit at AMD 16
April 28-29, 2010

17. Stefano's GIT branches
 git://xenbits.xen.org/people/sstabellini/linux-pvhvm
 2.6.32-pvhvm – development branch
Xen Summit at AMD 17
April 28-29, 2010