Re: [Xen-devel] HVM domains crash after upgrade from XEN 4.5.1 to 4.5.2

[Doug Goldstein <cardoe@xxxxxxxxxx>]

On 11/14/15 6:14 PM, Atom2 wrote:
> 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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

I'm a little late to the thread but can you send me (you can do it
off-list if you'd like) the USE flags you used for xen, xen-tools and
seabios? Also emerge --info. You can kill two birds with one stone by
using emerge --info xen.

I'm not too familiar with the xen ebuilds but I was pretty sure that
xen-tools is what builds hvmloader and it downloads a copy of SeaBIOS
and builds it so that it remains consistent. But obviously your
experience shows otherwise.

I'm looking at some ideas to improve SeaBIOS packaging on Gentoo and
your info would be helpful.

-- 
Doug Goldstein

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