32-bit ARM guest on 64-bit ARM Xen

[Robert VanVossen <robert.vanvossen@dornerworks.com>]

Hello,

I was wondering, what is the current state of running a 32-bit ARM guest running
on a 64-bit Xen for ARM. I was working on getting the minios from
https://github.com/talex5/xen/commits/next built and running as a guest on an
emulated Cortex-A53. I have gotten Xen and 64-bit Linux guests running in the
emulated environment, but I ran into some issues with the 32-bit guests.

When I tried to run them, I got the following:

Parsing config from /etc/xen/mini.cfg
(XEN) Hypervisor Trap. HSR=0x2000000 EC=0x0 IL=1 Syndrome=0x0
(XEN) CPU0: Unexpected Trap: Hypervisor
(XEN) ----[ Xen-4.6-unstable  arm64  debug=y  Not tainted ]----
(XEN) CPU:    0
(XEN) PC:     00000000002413c8 schedule_tail+0x248/0x2dc
(XEN) LR:     0000000000241300
(XEN) SP:     000080003ef5fe80
(XEN) CPSR:   600003c9 MODE:64-bit EL2h (Hypervisor, handler)
(XEN)      X0: 0000000000000000  X1: 0000000000000000  X2: 0000000000000000
(XEN)      X3: 0000000000000000  X4: 0000000000000000  X5: 0000000000000008
(XEN)      X6: 0000000040011100  X7: 0000000000000000  X8: 000080003ef632e0
(XEN)      X9: 000080003ef5feb0 X10: 0000000100000000 X11: aea06b1800000000
(XEN)     X12: 000000000000007f X13: 2f3b52d000000000 X14: 0000000100000000
(XEN)     X15: 0000007fae98c598 X16: 0000000000000024 X17: 0000007fae908b50
(XEN)     X18: 0000007ffb53e170 X19: 000080003efdb000 X20: 000080003ef63000
(XEN)     X21: 0000000000000000 X22: 0000000000000000 X23: 0000000000000000
(XEN)     X24: 0000000000000000 X25: 0000000000000000 X26: 0000000000000000
(XEN)     X27: 0000000000000000 X28: 0000000000000000  FP: 000080003ef5fe80
(XEN)
(XEN)   VTCR_EL2: 80023558
(XEN)  VTTBR_EL2: 000200003ef66000
(XEN)
(XEN)  SCTLR_EL2: 30cd187d
(XEN)    HCR_EL2: 000000000038643f
(XEN)  TTBR0_EL2: 000000003eef4000
(XEN)
(XEN)    ESR_EL2: 02000000
(XEN)  HPFAR_EL2: 0000000000f90100
(XEN)    FAR_EL2: ffffff8000000f00
(XEN)
(XEN) Xen stack trace from sp=000080003ef5fe80:
(XEN)    000080003ef5fea0 0000000000241468 0000000000000000 0000000000000000
(XEN)    0000000000000000 000000000024145c 0000000000000000 00000000ffffffff
(XEN)    0000000047fff000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000040008000 00000000000001d3
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN) Xen call trace:
(XEN)    [<00000000002413c8>] schedule_tail+0x248/0x2dc (PC)
(XEN)    [<0000000000241300>] schedule_tail+0x180/0x2dc (LR)
(XEN)    [<0000000000241468>] continue_new_vcpu+0xc/0xa4
(XEN)    [<000000000024145c>] continue_new_vcpu+0/0xa4
(XEN)
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) CPU0: Unexpected Trap: Hypervisor
(XEN)
(XEN) ****************************************
(XEN)
(XEN) Reboot in five seconds...

I was trying to figure out if it had to do with issues with mini-os in general,
or if it had to do with the fact that mini-os can currently only be built with
32-bit support. So I took a 32-bit linux kernel that had xen guest support
enabled. I tried to boot that guest, and I got the exact same error. I tried to
do some searching on the wiki and on the mailing list and I couldn't find any
references to this issue. Is this a known bug and are there any plans to fix this?

Thanks,
Robbie VanVossen
DornerWorks