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

["Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>]

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.

-- 
 Kirill A. Shutemov

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