Xen ARM TODO

This is a list of open work items and known bugs for the Xen on ARM with virtualization extension project.

Known Bugs

General

Domain 0 memory limitation due to 1:1 mapping

The use of the 1:1 workaround for dom0's memory (needed on platforms without an I/O SMMU, which is currently all) limits the maximum size of dom0. By carefully positioning the Xen and initial kernel/initrd/dtb binaries at the top of RAM dom0 is able to make use of up to 1/2 of the host RAM. The remainder is available for guest use. In general dom0 should be made quite small anyway. For more information see:

* http://lists.xen.org/archives/html/xen-devel/2013-12/msg02239.html
* http://lists.xen.org/archives/html/xen-devel/2014-01/msg00885.html

This should be addressed in a future release by supporting multiple memory banks for dom0.

Open Work Items

Save/restore and migration

Contact: xen-devel@lists.xen.org

Description: Make VM save/restore and VM migration work on ARM.

References: An initial prototype was written a couple of years ago for arm32 but never completed: http://lists.xen.org/archives/html/xen-devel/2013-10/msg00192.html

PCI device assignment to DomUs

Contact: xen-devel@lists.xen.org

Description: Assign one or more devices to an unprivileged guest, re-program the SMMU accordingly.

References: Not specified, useful references.

ITS support

Contact: xen-devel@lists.xen.org

Description: Physical and virtual ITS support for GICv3. References=Work underway: http://marc.info/?i=1426775889-29442-1-git-send-email-vijay.kilari%40gmail.com

References: Not specified, useful references.

Expose Wallclock time to guests

Contact: xen-devel@lists.xen.org

Description: Current Xen on ARM does not popular the wallclock time fields of the shared info with anything useful. It should do so...

References: Not specified, useful references.

More flexible early printk support

Contact: xen-devel@lists.xen.org

Description: Allow a single Xen binary to support multiple platforms for early_printk Rather than parsing the DTB early in asm to get the command line it would probably be sufficient to have a magic hex byte at a specific offset which could be edited by a simple tool.

References: http://lists.xen.org/archives/html/xen-devel/2014-02/msg01880.html

Support for DT /chosen/stdout-path node

Contact: xen-devel@lists.xen.org

Description: ePAPR 1.1 3.5 defines the /chosen/stdout-path property which contains the path to the serial device as a string. We could potentially make two uses of this: Xen itself could use this property if it is present to set the default dtuart= option, saving users the hassle. We could pass a suitable /chosen/stdout-path to dom0 to cause it to use hvc0 by default. This needs thinking through since hvc0 doesn't itself have a dt node.

References: https://www.power.org/documentation/epapr-version-1-1/ https://git.kernel.org/linus/a208ffd251d08ed7ba6bdf3ae1e423373fb12d3d https://git.kernel.org/linus/3482f2c52b77bf6596e24aae82e204a0603eba66

VCPU virtual time support

Contact: xen-devel@lists.xen.org

Description: Currently the concept of virtual time exposed to the guests is very simplistic and is just a static offset from physical time based on the time when the guest was started. We need to consider if this is actually what is needed/wanted and consider cases such as stolen time etc.

References: A patch series was sent to the LKML but never fully upstreamed: http://marc.info/?l=linux-arm-kernel&m=138929238127454&w=2