Problem with Fiasco under QEMU

Alexander Valitov valitov79 at
Tue Mar 17 17:17:21 CET 2009

Björn Döbel wrote:
> dm_phys is not able to allocate 64MB of memory for the Linux server. You
> may try passing Qemu the -m <memsize> option and thereby increase
> virtual machine memory.

Additional '-m 256' option helped. Default value for the option is 128. In
this case Roottask receives 87MB and biggest pool is 58MB. With '-m 256'
biggest pool is 175MB.

I also have found out that DOUBLE FAULT situation in Fiasco is cured by
turning off "Kernel options->Assembler IPC shortcut" Fiasco option. Does
someone know that causes the "DOUBLE FAULT"?
As seen from maillist archive it is a known problem, but I wonder why is it
still not fixed? Let me explain. Menuconfig says that "assembler IPC
shortcut" increases performance of short IPC (I guess it is IPC inside of an
address space). It is definitely a good thing and I'd like to have it turned
on. But it could causes crash in kernel (potentially also on hardware???).
It is definitely a bad thing. The excuses that I see is that fix is really
tricky and couldn't be easily implemented or the root of problem is known
and it triggers problem ONLY with QEMU.

Best Regards,
  Alexander Valitov

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