Re: [Xen-devel] Linux 4.19.5 fails to boot as Xen dom0

[Hans van Kranenburg <hans@xxxxxxxxxxx>]

On 11/30/18 5:21 PM, Kirill A. Shutemov wrote:
> On Fri, Nov 30, 2018 at 02:53:50PM +0000, Hans van Kranenburg wrote:
>> On 11/30/18 2:26 PM, Kirill A. Shutemov wrote:
>>> On Fri, Nov 30, 2018 at 01:11:56PM +0000, Hans van Kranenburg wrote:
>>>> On 11/29/18 4:06 PM, Kirill A. Shutemov wrote:
>>>>> On Thu, Nov 29, 2018 at 03:00:45PM +0000, Juergen Gross wrote:
>>>>>> On 29/11/2018 15:32, Kirill A. Shutemov wrote:
>>>>>>> On Thu, Nov 29, 2018 at 02:24:47PM +0000, Kirill A. Shutemov wrote:
>>>>>>>> On Thu, Nov 29, 2018 at 01:35:17PM +0000, Juergen Gross wrote:
>>>>>>>>> On 29/11/2018 14:26, Kirill A. Shutemov wrote:
>>>>>>>>>> On Thu, Nov 29, 2018 at 09:41:25AM +0000, Juergen Gross wrote:
>>>>>>>>>>> On 29/11/2018 02:22, Hans van Kranenburg wrote:
>>>>>>>>>>>> Hi,
>>>>>>>>>>>>
>>>>>>>>>>>> As also seen at:
>>>>>>>>>>>> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914951
>>>>>>>>>>>>
>>>>>>>>>>>> Attached there are two serial console output logs. One is starting 
>>>>>>>>>>>> with
>>>>>>>>>>>> Xen 4.11 (from debian unstable) as dom0, and the other one without 
>>>>>>>>>>>> Xen.
>>>>>>>>>>>>
>>>>>>>>>>>> [    2.085543] BUG: unable to handle kernel paging request at
>>>>>>>>>>>> ffff888d9fffc000
>>>>>>>>>>>> [    2.085610] PGD 200c067 P4D 200c067 PUD 0
>>>>>>>>>>>> [    2.085674] Oops: 0000 [#1] SMP NOPTI
>>>>>>>>>>>> [    2.085736] CPU: 1 PID: 1 Comm: swapper/0 Not tainted
>>>>>>>>>>>> 4.19.0-trunk-amd64 #1 Debian 4.19.5-1~exp1+pvh1
>>>>>>>>>>>> [    2.085823] Hardware name: HP ProLiant DL360 G7, BIOS P68 
>>>>>>>>>>>> 05/21/2018
>>>>>>>>>>>> [    2.085895] RIP: e030:ptdump_walk_pgd_level_core+0x1fd/0x490
>>>>>>>>>>>> [...]
>>>>>>>>>>>
>>>>>>>>>>> The offending stable commit is 
>>>>>>>>>>> 4074ca7d8a1832921c865d250bbd08f3441b3657
>>>>>>>>>>> ("x86/mm: Move LDT remap out of KASLR region on 5-level paging"), 
>>>>>>>>>>> this
>>>>>>>>>>> is commit d52888aa2753e3063a9d3a0c9f72f94aa9809c15 upstream.
>>>>>>>>>>>
>>>>>>>>>>> Current upstream kernel is booting fine under Xen, so in general the
>>>>>>>>>>> patch should be fine. Using an upstream kernel built from above 
>>>>>>>>>>> commit
>>>>>>>>>>> (with the then needed Xen fixup patch 1457d8cf7664f34c4ba534) is 
>>>>>>>>>>> fine,
>>>>>>>>>>> too.
>>>>>>>>>>>
>>>>>>>>>>> Kirill, are you aware of any prerequisite patch from 4.20 which 
>>>>>>>>>>> could be
>>>>>>>>>>> missing in 4.19.5?
>>>>>>>>>>
>>>>>>>>>> I'm not.
>>>>>>>>>>
>>>>>>>>>> Let me look into this.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> What is making me suspicious is the failure happening just after
>>>>>>>>> releasing the init memory. Maybe there is an access to .init.data
>>>>>>>>> segment or similar? The native kernel booting could be related to the
>>>>>>>>> usage of 2M mappings not being available in a PV-domain.
>>>>>>>>
>>>>>>>> Ahh.. Could you test this:
>>>>>>>>
>>>>>>>> diff --git a/arch/x86/mm/dump_pagetables.c 
>>>>>>>> b/arch/x86/mm/dump_pagetables.c
>>>>>>>> index a12afff146d1..7dec63ec7aab 100644
>>>>>>>> --- a/arch/x86/mm/dump_pagetables.c
>>>>>>>> +++ b/arch/x86/mm/dump_pagetables.c
>>>>>>>> @@ -496,7 +496,7 @@ static inline bool is_hypervisor_range(int idx)
>>>>>>>>         * ffff800000000000 - ffff87ffffffffff is reserved for
>>>>>>>>         * the hypervisor.
>>>>>>>>         */
>>>>>>>> -      return  (idx >= pgd_index(__PAGE_OFFSET) - 16) &&
>>>>>>>> +      return  (idx >= pgd_index(__PAGE_OFFSET) - 17) &&
>>>>>>>>                (idx <  pgd_index(__PAGE_OFFSET));
>>>>>>>>  #else
>>>>>>>>        return false;
>>>>>>>
>>>>>>> Or, better, this:
>>>>>>
>>>>>> That makes it boot again!
>>>>>>
>>>>>> Any idea why upstream doesn't need it?
>>>>>
>>>>> Nope.
>>>>>
>>>>> I'll prepare a proper fix.
>>>>>
>>>>
>>>> Thanks for looking into this.
>>>>
>>>> In the meantime, I applied the "Or, better, this" change, and my dom0
>>>> boots again.
>>>>
>>>> FYI, boot log now: (paste 90d valid)
>>>> https://paste.debian.net/plainh/48940826
>>>
>>> I forgot to CC you:
>>>
>>> https://lkml.kernel.org/r/20181130121131.g3xvlvixv7mvlr7b@xxxxxxxxxxxxxxxxxx
>>>
>>> Please give it a try.
>>
>> I'm not in that thread, so my response here...
>>
>> You paste a v2-like patch into 'Re: [PATCH 1/2]'. Juergen says:
>> s/LDT_PGD_ENTRY/GUARD_HOLE_PGD_ENTRY/, then you say Ughh.., change it to
>> GUARD_HOLE_ENTRY, which does not exist, and then get a Reviewed-by from
>> Juergen.
>>
>> I guess it has to be GUARD_HOLE_PGD_ENTRY after all...
>>
>> arch/x86/include/asm/pgtable_64_types.h:116:31: error:
>> 'GUARD_HOLE_ENTRY' undeclared (first use in this function); did you mean
>> 'GUARD_HOLE_PGD_ENTRY'?
>>
>> I'll test that instead.
> 
> Yes, thank you. It was a long week... :/
> 
> Let me know if it works. I'll repost the fixed version with your
> Tested-by.

Ok. It boots fine as Xen dom0. \o/

You can use "Hans van Kranenburg <hans.van.kranenburg@xxxxxxxxxx>"
(lowercase please) for reported/tested in the real v2.

Hans


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