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Re: [Xen-users] Starting to port xen on beagleboard-x15 (GSoC 2019 project)

(+ Andre and Oleksandr)

Hi Denis & lain,

I have discussed with Andre Przywara (in CC) who did some work around virtualization support in U-boot.

I have also CCed Oleksandr, who IIRC worked on a platform using the same SoC (DRA7) in the past.

On 17/06/2019 10:03, Iain Hunter wrote:
I can't remember the history of that patch. What I couldn't figure out
today was what its effect would be.  I could not find any u-boot code
that used the CONFIG_XXX values added in the patch.
So, best ignore it.

lain, did you manage to get SMP working back then?

Do you have an emulator available yet?
If so the easiest way I found to debug this type of issue was to:

1. Insert an infinite loop just before where I thought I had a problem
    - in a .S file with
  loopHere: b loopHere

- in a C file with

volatile unsigned char loopHere=1;

{  ....

2 boot the board
3 connect the emulator to the target and then load the symbols for the
executable (u-boot.img or xen)
4 in the emulator set the PC to first instruction after the loop and
then step over the code. Then you can check the register values to see
if hypevisor is enabled etc

Both CPUs are Cortex-A15, hence virtualization should be supported. It is a matter of correctly initializing the secondary CPU.

The platform is not using PSCI but instead a custom SMP bring-up (see omap5_smp_init in Xen). From my understanding the ROM should bring-up the secondary CPU to hyp mode if the boot CPU is in hyp mode.

It would be interesting to try Linux on baremetal and see if it brings-up the secondary CPUs in hyp mode. If it does, then it seems that the problem lies in Xen. Otherwise it would be in the ROM.

On a side note, I would not spend too much time looking at the SMP now. Instead you can disable the secondary CPUs.


Julien Grall

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