[GSoC] Paravirtualization Layer - test on L4Re

Gedare Bloom gedare at rtems.org
Mon Sep 23 13:16:51 UTC 2013

Sounds good. Would it be a BSP for each hypervisor for each target CPU
type the hypervisor runs on?


On Mon, Sep 23, 2013 at 9:10 AM, Philipp Eppelt
<philipp.eppelt at mailbox.tu-dresden.de> wrote:
> Hi,
> 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.
> Cheers
> Philipp
> 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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