Re: 32-bit ARM guest on 64-bit ARM Xen

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

On 4/28/2015 4:14 PM, Julien Grall wrote:
> 
> On 28/04/2015 20:14, Robert VanVossen wrote:
>> Hello,
> 
> Hi Robert,
> 
>> 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.
> 
> I used 32-bit kernel on 64-bit hardware recently without no issue. 
> AFAICT, 32-bit guest as always worked on Xen. Which version on Xen are 
> you running?
> 
I thought that should be the case, but I couldn't find confirmation anywhere
online.

I am building from master, more specifically commit 123c7793...

> Also, silly question, does your hardware supports 32-bit instructions? 
> I.e were you able to run Linux 32-bit on baremetal?
> 

I had assumed that all cortex-A53 implementations had to support 32-bit
instructions, but that might not be the case. At least, the emulated model might
not. I will have to look more into that.

>> 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
> 
> This looks like an issue with Xen running on your hardware. EC = 0x0 
> means "Exception with an Unkwnown reasons".
> 
>> (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
> 
> schedule_tail contains the code to context switch from one domain to 
> another one.
> 
> Can you run addr2line on the xen-syms with the address in PC and give 
> the result?
> 
This yields xen/xen/arch/arm/domain.c:208 which has the following line:

WRITE_SYSREG32(n->arch.teecr, TEECR32_EL1);

Thanks,
Robbie VanVossen