Re: [Xen-devel] [ARM] Bash often segfaults in Dom0 with the latest Xen

[Christoffer Dall <christoffer.dall@xxxxxxxxxx>]

On 5 June 2013 10:53, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> On 06/05/2013 06:36 PM, Christoffer Dall wrote:
>
>>>
>>> I'm using the linaro's branch ll_20130528.0, I have only few patches for
>>> the dts and not yet in linaro tree patches.
>>>
>>> I have the same issue with linux 3.9-rc4 with multiple CPUs and I can't
>>> really go before without carrying many xen patches to try it.
>>>
>>> I have tried different configuration with the number of CPUs in Xen
>>> (pCPU) and linux (vCPU):
>>>   - 2 pCPU 2 vCPU : segfaulting
>>>   - 2 pCPU 1 vCPU : working
>>>   - 1 pCPU 1 vCPU : working
>>>   - 1 pCPU 2 vCPU : very slow but working
>>>
>> 2 pCPU 1 vCPU are you still compiling your dom0 as an SMP kernel, but
>> only creating 1 vCPU or are you actually compiling the dom0 as UP?
>
>
> Yes. It's same kernel with the same command line (ie without nosmp).
> I have limited the number of dom0 vcpus with dom0_max_vcpus=1 on xen
> command line.
>
It indicates a bug in Xen then. Curious that it only happens for user
space in dom0, but perhaps you just haven't seen it in the kernel yet.
Bash scripts are pretty intensive on page faults so perhaps there's a
synchronization issue with some of your page fault handlers.

You could try to touch all the memory inside dom0 (dd to a ramfs for
example) and then run your bash script and see if the problem still
occurs, that should point you to whether it's a stage-2 fault handling
issue, but this is not a fool-proof approach. Maybe Xen can
pre-allocate all the stage-2 entries?

-Christoffer

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