On Fri, Jul 22, 2016 at 03:26:01PM +0200, Franco Fichtner wrote:
> Hi,
>
> With a client we're running into the following boot panic
> since upgrading from 5.7 to 5.9 on a specific Hyper-V guest:
>
> cpu0: Intel(R) Xeon(R) CPU E5420 @ 2.50GHz ("GenuineIntel" 686-class) 1.65 GHz
> cpu0:
> FPU,V86,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CF
> LUSH,MMX,FXSR,SSE,SSE2,SS,HTT,NXE,LONG,SSE3,SSSE3,CX16,SSE5.1,XSAVE,HV,LAHF
> [...]
> kernel: protection fault trap, code=0
> Stopped at cpu_paenable+0x20: movl %edi,%cr3
>
> This happens consistently, but we have other clients that
> run Hyper-V without a problem on 5.9 now.
>
> Looking for a clue I dug through the commits and found that
> reviving pmap_bootstrap_pae() in April 2015 caused this, and
> reverting boots said Hyper-V guest just fine.
>
> Hyper-V is on the latest version and we could not find a
> reason why said guest / host pair behaves that way.
>
> I have two questions:
>
> (1) Since NX/PAE is pretty much standard on all hardware from
> the last +15 years and is now used to enforce W^X, are there
> going to be problems *not* running that code either now or in
> the future?
>
> (2) Could this be something to be fixed in the i386 assembler
> code in cpu_paenable?
>
> It's difficult to get dumps / screen caps from the system or
> run commands in ddb, but if there's interest I will try to
> provide the requested info.
>
>
> Cheers,
> Franco
Certainly odd. I'll try to reproduce this (since I was the one who
brought PAE/NX back into the i386 picture last year). It should work
fine (this is the first report I've seen about crashing there).
What is your Hyper-V server host environment? Server 2012 R2? And I
need a full dmesg from when this worked, please.
It's also possible this is a Hyper-V bug. We've seen those as well
and had to work around them also.
-ml
