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

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

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?
Given that I am compiling from source under gentoo and provided you lend 
me a helping hand in case I get stuck, I am confident that this is possible.

gentoo has three xen packages (they call those ebuilds) as follows
     app-emulation/xen
     app-emulation/xen-tools
     app-emulation/pvgrub
all of which are installed on my system. The former two offer a debug 
USE-flag and I assume that debug code for the latter is not required as 
this is for (the still working) PV domUs only. Furthermore as you are 
talking about the hypervisor, I guess it is safe to assume that it is 
app-emulation/xen and not xen-tools. Right?

BTW: The description of the debug USE flag reads as follows:
Enable extra debug codepaths, like asserts and extra output. If you want 
to get meaningful backtraces see 
https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
I assume that backtraces are probably not required to get things moving.

Another question is whether prior to enabling the debug USE flag it 
might make sense to re-compile with gcc-4.8.5 (please see my previous 
list reply) to rule out any compiler related issues. Jan, Andrew - what 
are your thoughts?

Many thanks Atom2