Problem with Fiasco under QEMU

Adam Lackorzynski adam at
Wed Mar 18 00:11:21 CET 2009

On Tue Mar 17, 2009 at 09:17:21 -0700, Alexander Valitov wrote:
> 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).

Nope, register only IPC is meant here.

> 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.

I basically can only remember seeing this on Qemu and as it does not
really matter there it probably does not make much sense in hunting
this one, besides that it's a tricky one. It may be different if it
happens on real hardware but still the easy work around is just
switching it off.

Adam                 adam at

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