Re: [Xen-devel] crash on boot with 4.6.1 on fedora 24

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 05/09/2016 01:22 PM, Kevin Moraga wrote:
>
> On 05/09/2016 11:15 AM, Boris Ostrovsky wrote:
>> On 05/09/2016 12:40 PM, Kevin Moraga wrote:
>>> On 05/09/2016 09:53 AM, Jan Beulich wrote:
>>>>>>> On 09.05.16 at 16:52, <kmoragas@xxxxxxxxxx> wrote:
>>>>> On 05/09/2016 04:08 AM, Jan Beulich wrote:
>>>>>>>>> On 09.05.16 at 00:51, <kmoragas@xxxxxxxxxx> wrote:
>>>>>>> I'm try to compile kernel 4.4.8 (using fedora 23) to run with Xen 4.6.0
>>>>>>> and Intel Skylake processor (Intel Core i7-6600U)
>>>>>>>
>>>>>>> This kernel is crashing almost in the same way as explained in this
>>>>>>> thread... But my problem is mainly with Skylake. Because the same
>>>>>>> configuration works within another machine but with another processor
>>>>>>> (Intel Core i5-3340M). Attached are the boot logs.
>>>>>> The address the fault occurs on (ffff8000006bdee0) is bogus, so
>>>>>> from the register and stack dump alone I don't think we can derive
>>>>>> much. What we'd need is access to the kernel binary used (or
>>>>>> really the vmlinux accompanying the vmlinuz that was used), in
>>>>>> order to see where exactly the kernel died, and hence where this
>>>>>> bogus address originates from. As I understand it this is a kernel
>>>>>> you built yourself - can you make said binary from exactly that
>>>>>> build available somewhere? 
>>>>> Yes I have it. But I get the same crash on various 4.4.X and also with
>>>>> 4.5.3.
>>>>>
>>>>> **https://drive.google.com/open?id=0B6Ol0ob95UxXQV9HM1BWMmhCZ0E 
>>>> Well, this doesn't contain the file I'm after (vmlinux), and taking
>>>> apart vmlinuz would be quite cumbersome.
>>>>
>>>> Jan
>>>>
>>> Oh sorry, here is the link to vmlinux
>>>
>>> https://drive.google.com/file/d/0B6Ol0ob95UxXN0dDMWM1a29vMEk/view?usp=sharing
>> This is still vmlinuz but the failure is at
>>
>> ffffffff81007ef3:       48 3b 1d 4e 2e ec 00    cmp   
>> 0xec2e4e(%rip),%rbx        # 0xffffffff81ecad48
>> ffffffff81007efa:       73 51                   jae    0xffffffff81007f4d
>> ffffffff81007efc:       31 c0                   xor    %eax,%eax
>> ffffffff81007efe:       48 8b 15 03 d2 c0 00    mov   
>> 0xc0d203(%rip),%rdx        # 0xffffffff81c15108
>> ffffffff81007f05:       90                      nop
>> ffffffff81007f06:       90                      nop
>> ffffffff81007f07:       90                      nop
>> ffffffff81007f08:       4c 8b 2c da             mov   
>> (%rdx,%rbx,8),%r13    <======
>> ffffffff81007f0c:       90                      nop
>> ffffffff81007f0d:       90                      nop
>> ffffffff81007f0e:       90                      nop
>> ffffffff81007f0f:       85 c0                   test   %eax,%eax
>> ffffffff81007f11:       78 3a                   js     0xffffffff81007f4d
>> ffffffff81007f13:       48 8b 05 ee 11 d2 00    mov   
>> 0xd211ee(%rip),%rax        # 0xffffffff81d29108
>> ffffffff81007f1a:       49 39 c5                cmp    %rax,%r13
>> ffffffff81007f1d:       73 6f                   jae    0xffffffff81007f8e
>> ffffffff81007f1f:       48 8b 05 ea 11 d2 00    mov   
>> 0xd211ea(%rip),%rax        # 0xffffffff81d29110
>> ffffffff81007f26:       4a 8b 04 e8             mov    (%rax,%r13,8),%rax
>>
>> Any chance you could provide an un-stripped binary or System.map?
> Here is the link for System.map
>
> https://drive.google.com/file/d/0B6Ol0ob95UxXYVE4SzdMcENsWWs/view?usp=sharing
>


So my semi-educated guess at your stack is
__early_ioremap
  -> __early_set_fixmap
    -> set_pte
      -> xen_set_pte_init
        -> mask_rw_pte
          -> pte_pfn
            -> pte_val
               -> xen_pte_val
                 -> pte_mfn_to_pfn
                   -> mfn_to_pfn_no_overrides
                     -> ret =
xen_safe_read_ulong(&machine_to_phys_mapping[mfn], &pfn)


With ffffffff81007f08 being the faulted address the last one looks
plausible:


ffffffff81007efe:       48 8b 15 03 d2 c0 00    mov   
0xc0d203(%rip),%rdx        # 0xffffffff81c15108
ffffffff81007f05:       90                      nop
ffffffff81007f06:       90                      nop
ffffffff81007f07:       90                      nop
ffffffff81007f08:       4c 8b 2c da       mov    (%rdx,%rbx,8),%r13

since

ostr@workbase> grep  ffffffff81c15108
/tmp/System.map-4.4.8-9.pvops.qubes.x86_64
ffffffff81c15108 D machine_to_phys_mapping
ostr@workbase>

But %rdx is not ffffffff81c15108, it is ffff800000000000:

(XEN) rax: 0000000000000000   rbx: 00000000000d7bdc   rcx: ffff880002059000
(XEN) rdx: ffff800000000000   rsi: 80000000d7bdc063   rdi: 80000000d7bdc063

Perhaps we jumped to ffffffff81007f08 from somewhere, but I can't 
ffffffff81007f0* as a target anywhere.


-boris
              


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