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

[Christoffer Dall <christoffer.dall@xxxxxxxxxx>]

On 5 June 2013 11:01, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Wed, 5 Jun 2013, Christoffer Dall wrote:
>> 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?
>
> Xen pre-allocates all the memory for stage-2 entries (no overcommit or
> populate on demand by default)

what was the conclusion when pinning the vcpu to dedicated pcpus - did
the error still show up?

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