Re: HVM domains crash after upgrade from XEN 4.5.1 to 4.5.2

[Atom2 <ariel.atom2@web2web.at>]

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Am 14.11.15 um 21:32 schrieb Andrew Cooper:
> On 14/11/2015 00:16, Atom2 wrote:
>> Am 13.11.15 um 11:09 schrieb Andrew Cooper:
>>> On 13/11/15 07:25, Jan Beulich wrote:
>>>>>>> On 13.11.15 at 00:00,<ariel.atom2@web2web.at>  wrote:
>>>>> Am 12.11.15 um 17:43 schrieb Andrew Cooper:
>>>>>> On 12/11/15 14:29, Atom2 wrote:
>>>>>>> Hi Andrew,
>>>>>>> thanks for your reply. Answers are inline further down.
>>>>>>>
>>>>>>> Am 12.11.15 um 14:01 schrieb Andrew Cooper:
>>>>>>>> On 12/11/15 12:52, Jan Beulich wrote:
>>>>>>>>>>>> On 12.11.15 at 02:08,<ariel.atom2@web2web.at>  wrote:
>>>>>>>>>> After the upgrade HVM domUs appear to no longer work - regardless
>>>>>>>>>> of the
>>>>>>>>>> dom0 kernel (tested with both 3.18.9 and 4.1.7 as the dom0 kernel); PV
>>>>>>>>>> domUs, however, work just fine as before on both dom0 kernels.
>>>>>>>>>>
>>>>>>>>>> xl dmesg shows the following information after the first crashed HVM
>>>>>>>>>> domU which is started as part of the machine booting up:
>>>>>>>>>> [...]
>>>>>>>>>> (XEN) Failed vm entry (exit reason 0x80000021) caused by invalid guest
>>>>>>>>>> state (0).
>>>>>>>>>> (XEN) ************* VMCS Area **************
>>>>>>>>>> (XEN) *** Guest State ***
>>>>>>>>>> (XEN) CR0: actual=0x0000000000000039, shadow=0x0000000000000011,
>>>>>>>>>> gh_mask=ffffffffffffffff
>>>>>>>>>> (XEN) CR4: actual=0x0000000000002050, shadow=0x0000000000000000,
>>>>>>>>>> gh_mask=ffffffffffffffff
>>>>>>>>>> (XEN) CR3: actual=0x0000000000800000, target_count=0
>>>>>>>>>> (XEN)      target0=0000000000000000, target1=0000000000000000
>>>>>>>>>> (XEN)      target2=0000000000000000, target3=0000000000000000
>>>>>>>>>> (XEN) RSP = 0x0000000000006fdc (0x0000000000006fdc)  RIP =
>>>>>>>>>> 0x0000000100000000 (0x0000000100000000)
>>>>>>>>> Other than RIP looking odd for a guest still in non-paged protected
>>>>>>>>> mode I can't seem to spot anything wrong with guest state.
>>>>>>>> odd? That will be the source of the failure.
>>>>>>>>
>>>>>>>> Out of long mode, the upper 32bit of %rip should all be zero, and it
>>>>>>>> should not be possible to set any of them.
>>>>>>>>
>>>>>>>> I suspect that the guest has exited for emulation, and there has been a
>>>>>>>> bad update to %rip.  The alternative (which I hope is not the case) is
>>>>>>>> that there is a hardware errata which allows the guest to accidentally
>>>>>>>> get it self into this condition.
>>>>>>>>
>>>>>>>> Are you able to rerun with a debug build of the hypervisor?
[big snip]
>>>>>>> Now _without_ the debug USE flag, but with debug information in
>>>>>>>          the binary (I used splitdebug), all is back to where the problem
>>>>>>>          started off (i.e. the system boots without issues until such
>>>>>>>          time it starts a HVM domU which then crashes; PV domUs are
>>>>>>>          working). I have attached the latest "xl dmesg" output with the
>>>>>>>          timing information included.
>>>>>>>   
>>
>> I hope any of this makes sense to you.
>>
>> Again many thanks and best regards
>>
>
> Right - it would appear that the USE flag is definitely not what you 
> wanted, and causes bad compilation for Xen.  The do_IRQ disassembly 
> you sent is a the result of disassembling a whole block of zeroes.  
> Sorry for leading you on a goose chase - the double faults will be the 
> product of bad compilation, rather than anything to do with your 
> specific problem.
Hi Andrew,
there's absolutely no need to appologize as it is me who asked for help 
and you who generously stepped in and provided it. I really do 
appreciate your help and it is for me, as the one seeking help, to 
provide all the information you deem necessary and you ask for.
> However, the final log you sent (dmesg) is using a debug Xen, which is 
> what I was attempting to get you to do originally.
Next time I know better how to arrive at a debug XEN. It's all about 
learning.
> We still observe that the VM ends up in 32bit non-paged mode but with 
> an RIP with bit 32 set, which is an invalid state to be in. However, 
> there was nothing particularly interesting in the extra log information.
>
> Please can you rerun with "hvm_debug=0xc3f", which will cause far more 
> logging to occur to the console while the HVM guest is running.  That 
> might show some hints.
I haven't done that yet - but please see my next paragraph. If you are 
still interested in this, for whatever reason, I am clearly more than 
happy to rerun with your suggested option and provide that information 
as well.
> Also, the fact that this occurs just after starting SeaBIOS is 
> interesting.  As you have switched versions of Xen, you have also 
> switched hvmloader, which contains the SeaBIOS binary embedded in it.  
> Would you be able to compile both 4.5.1 and 4.5.2 and switch the 
> hvmloader binaries in use.  It would be very interesting to see 
> whether the failure is caused by the hvmloader binary or the 
> hypervisor.  (With `xl`, you can use 
> firmware_override="/full/path/to/firmware" to override the default 
> hvmloader).
Your analysis was absolutely spot on. After re-thinking this for a 
moment, I thought going down that route first would make a lot of sense 
as PV guests still do work and one of the differences to HVM domUs is 
that the former do _not_ require SeaBIOS. Looking at my log files of 
installed packages confirmed an upgrade from SeaBIOS 1.7.5 to 1.8.2 in 
the relevant timeframe which obviously had not made it to the hvmloader 
of xen-4.5.1 as I did not re-compile xen after the upgrade of SeaBIOS.

So I re-compiled xen-4.5.1 (obviously now using the installed SeaBIOS 
1.8.2) and the same error as with xen-4.5.2 popped up - and that seemed 
to strongly indicate that there indeed might be an issue with SeaBIOS as 
this probably was the only variable that had changed from the original 
install of xen-4.5.1.

My next step was to downgrade SeaBIOS to 1.7.5 and to re-compile 
xen-4.5.1. Voila, the system was again up and running. While still 
having SeaBIOS 1.7.5 installed, I also re-compiled xen-4.5.2 and ... you 
probably guessed it ... the problem was gone: The system boots up with 
no issues and everything is fine again.

So in a nutshell: There seems to be a problem with SeaBIOS 1.8.2 
preventing HVM doamins from successfully starting up. I don't know what 
this is triggered from, if this is specific to my hardware or whether 
something else in my environment is to blame.

In any case, I am again more than happy to provide data / run a few 
tests should you wish to get to the grounds of this.

I do owe you a beer (or any other drink) should you ever be at my 
location (i.e. Vienna, Austria).

Many thanks again for your analysis and your first class support. Xen 
and their people absolutely rock!

Atom2

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