Re: KVM 12 and BUG with preempt kernel

Avi Kivity
2007-01-24T16:53:33Z

roucaries bastien wrote:
>>
>> > Nethertheless I think it is time to report
>> > another bug (present without this patch therefore unrelated).
>> > Unfortunatly I have no trace because it crash my machine and I do not
>> > manage to find it.
>> >
>> > If I booot my debian guest with framebuffer activated after 20s to 15
>> > minutes I see on my host screen a cloud of colorfull pixel. These
>> > pixel flash and seems related to guest frame buffer (same colors
>> > scheme but because it not the same resolution I can't read it). About
>> > 3s latter my box crash and is dead (cap lock does not even toggles the
>> > keyboard led). Therefore it seems that the guest achieve to write the
>> > host memory :-(, the good point is that he does not poke to my hard
>> > drive registers.
>> >
>> > This behavior is 100% reproductible. If I run the host and I switch to
>> > the text console I can't even get a trace because the screen is
>> > corrupted.
>>
>>
>> You can start the guest in vnc mode (-vnc 1), so the host can remain in
>> text mode, or use netconsole.
> The problem is not switching between x and console but read the oops
> because kvm write to video mem :-(. And I do not think netconsole
> could help because my computer does not answer to irq, I suspect
> something nasty. The only think that could help is nmi watchdog but
> unfortunatly the bios declare timer interupt as XT-pic and not io-apic
> (bios bug forwaded to asus), therefore no nmi.
>
> Moreover I try vnc switch and kvm is stable, stange isn't.
>
> To reproduce:
> - use an preempt host kernel on amd64, kvm compiled as x86_64

Which host kernel version are you using?

> - install a testing debian on a guest using sdl display, use
> framebuffer install (default)

Please provide a link to the installer so I can try it too.

> - wait....
> - when you see colorfull pixel on the top of your sceen, kill kvm
> (kill only accelerate the crash)
> - wait 1s
> - kernel will crash
>
> I suspect I am seeing this colorfull pixel because I use a vesa driver
> on X and the guest write to it.

No, the guest cannot write directly to host memory. It writes to a
virtualized framebuffer.

--
error compiling committee.c: too many arguments to function