[GSoC] Paravirtualization Layer - test on L4Re

Philipp Eppelt philipp.eppelt at mailbox.tu-dresden.de
Mon Sep 23 13:10:06 UTC 2013


in the last days I reused my work on L4RTEMS to do a quick and dirty
test of the new virtualization layer.

The implementation -which isn't working yet- showed, that we the
i386/virtualpok BSP is a very good point to start, but the vCPU
interface of L4Re brings it's own dependencies which must be added to
include/ and in Makefile.am.
I also had to extend the virtualizationalyerbsp.h file with these
includes and a structure shared between L4Re and RTEMS. This struct
accommodates a vCPU and console capability and a pointer to the vCPU
state. They are filled in at start up by L4Re and can then be used by RTEMS.

The take away are two things:
First, we might end up with an own BSP for each hypervisor.
Second, as far as I can see now, they only differ in aspects of the
layer, not in the drivers using the layer.

The code isn't on github yet, as I am short on time and have to sort
things out first. The obstacle at the moment is to create a library in
L4Re, which includes all L4Re dependencies and has only a few undefined
references, which can be resolved by RTEMS.


On 09/20/2013 09:22 AM, Philipp Eppelt wrote:
> Hi,
> what did I do in my project?
> I designed and implemented a virtualization layer, which should ease the
> virtualization of RTEMS across different hypervisors.
> To test the layer and because of the ARINC 653 compliance POK was chosen
> as a proof-of-concept host OS.
> The project was a partial success. The layer is designed, implemented
> and a BSP is using it, and it is at least partially working.
> I didn't succeed in changing POK so it can forward interrupts to
> partitions reliably.  But this is an POK related issue, which I think
> won't be an issue on a host OS providing a vCPU abstraction. Also
> implementing this for other architectures might be easier than for x86.
> A console is printing hello World and sometimes under some circumstances
> the base_sp sample printed output, too. But the latter is not reliable.
> I have documented my efforts, including implementation issues, GDB traps
> and where I left off on the wiki page [0].
> Also explanations on how to port the i386/virtualpok BSP to other
> hypervisors and how to port this approach to other architectures can be
> found there. The latter is pretty abstract, as I don't know much about
> the other architectures(arm, ppc, sparc).
> I provide two patches:
> * Split of the i386 CPU between score/cpu and libcpu. The interrupt
> handling was moved to libcpu and two new CPU variants were introduced
> there: Native and virtual. The native one works like before but the
> virtual one calls the virtualization layer instead of executing cli,sti
> or hlt. The list of affected functions is documented in the wiki[0].
> BUT: This patch won't be merged, as includes in cpukit from libcpu
> aren't allowed (but it works). But before the discussion about a new
> configuration option isn't finished and the option is implemented there
> is no other way to achieve this.
> * A new i386 BSP is introduced: virtualpok. It is the corresponding BSP
> to the virtual i386 CPU model and brings along the virtualization layer
> as two header files in it's include/ directory. A console driver, clock
> driver and IRQ management is implemented and as far as possible tested
> on POK.
> If you have questions on the work, I'd be happy to answer them.
> Cheers,
> Philipp
> [0]
> http://wiki.rtems.org/wiki/index.php/GSOC_2013_-_Paravirtualization_of_RTEMS
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