Re: [Qemu-devel] problem with 64/64 guest running grub

[Werner Dittmann]

Doing some more tests and trying to get more info about the problem
shows some common behaviours:

- the problems are with the x86_64 emulation regardless if it is
  running on a 32bit or 64bit host (in my case always Linux host)

- The problems happen in all qemu modes: no kqemu, user kqemu, kernel
  kqemu. The main difference: happens on different times during the
  installation process

- It happens (at least this is what I can see) only if the 64 bit kernel
  that runs in qemu-system-x86_64 executes a 32 bit application. For
  example grub is a 32 bit application that runs in the 64bit kernel,
  some installation programs (at least in Suse) are also 32bit applications.

The last statement is supported by the following oberservation: when
Qemu crashes or hangs I very often see some strange register values, for
example:

RBX=ffffffff80523028
RSP=ffffffff80522dc0
RIP=ffffffff8025e67c

If you remove the ff s then you have e.g. a instrution pointer address
that is usually a valid address of a 32bit environment. IMHO something
could be wrong with 32bit support inside qemu-system-x86_64.

Any more ideas where to look to "embrace" the problem?

Regards,
Werner


Werner Dittmann wrote:
> Same happen to Suse 64 host/64 guest system (Suse 10.1). A 32-bit
> guest system install quite well.
> 
> My trace shows the same symptom: Qemu seems to loop in a very tight
> loop. Sometimes (using infoe registers rapidly) I can even see that
> it seems to switch to 32bit mode inside the guest kernel maybe because
> a 32 bit application is running?
> 
> No kqemu is involved when running the 64bit guest, started with
> -no-kqemu.
> 
> As mike wrote: any hint how I can help to tackle the problem is
> appreciated.
> 
> 
> Regards,
> Werner
> 
> 
> Mike Day wrote:
>> I'm having a problem with qemu (cvs and 0.8.2) running on a 64 bit
>> athlon x2 with a 64 bit guest. When installing edgy in a new 64-bit
>> guest, the guest always freezes when installing grub on the boot
>> partition.
>> This only happens with a 64/64 system. I can run the guest in qemu (as
>> opposed to
>> qemu-system-x86_64) and use grub to install itself, but if I try to do
>> the same thing with qemu-system-x86_64 it hangs.
>> After generating a trace file and stepping through the hang in gdb it
>> looks like the guest is getting overwhhelmed with interrupts. It
>> reminds me of a situation where some device driver is forgetting to
>> issue an eoi and the interrupt line is remaining on, which means that
>> the guest can never make any progress advancing the instruction
>> pointer.
>>
>> I've placed a compressed log file at
>> http://www.ncultra.org/qemu.log.tgz
>>
>> I'd be happy to spend some more time runnign this down - if anyone has
>> any suggestions on how I should proceed I'd be grateful.
>> Mike
>>
>>
> 
> 
> 
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