seems I finally found what upset kqemu on amd64 SMP... shared gdt! (please test new patch :)

Juergen Lock nox at
Sun May 11 21:09:55 UTC 2008

On Sun, May 11, 2008 at 12:27:45PM -0700, Bakul Shah wrote:
> Juergen,
> With your latest patch things are looking pretty good!
> - Multiple qemus on a MP FreeBSD amd64 works with kqemu
>   enabled for user code.  Some running 64 bit kernels
>   (freebsd), some running 32 bit kernels (freebsd and plan9).
> - Nested qemus work! That is, qemu*x86_64 under qemu*x86_64,
>   both with user mode kqemu. A 32 bit 7.0 kernel under it ran
>   fine.  Ideally qemus should nest as long as there is enough
>   memory (a torture test for emulation fidelity).
> - As mentioned in another thread netbooting works well enough
>   but you have to use pxeboot from -current and append a byte
>   to it to work around an etherboot tftp bug.
> Now the bugs (probably most having to do with qemu/kqemu,
> not the freebsd port):
> 1. kernel mode kqemu seems to cause crashes.  Generally this
>    happens right after the guest freebsd kernel comes up.
Yeah I posted one of those on the qemu list,

 32 bit linux guests seem to work fine tho at least.

> 2. After the above crash VM reboots automatically but now it
>    can't find the root device so it hangs at the root
>    selection prompt.

> 3. Ocassionally plan9 and (less often FreeBSD) crashes on
>    boot.  Looks like a race condition of some sort.  If they
>    boot, there are no further problems traceable to
>    qemu/kqemu.

> 4. "calcru: runtime went backwards from <t1> usec to <t2> for
>    pid <pid> (<cmd>)" is back!

 Well, the clock never was very accurate thats true...

>    Also, ntpd seems to get very
>    confused and after syncing with another clock shifts
>    mostly correct time by a few hours.

> 5. An initial getty gets killed as it "exceeded maximum CPU limit"
>    This could an emulation bug or related to time issues.
> Random thoughts:
> - If qemu is made scriptable we can automate a lot of
>   testing.  For qemu/kqemu and freebsd.
 Hmm what exactly do you want to script there?

> - We need to add a section on qemu in the handbook.

 Hmmm... :)


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