Re: [Qemu-devel] [BUG] Guest kernel divide error in kvm_unlock_kick

[Chris Webb]

Paolo Bonzini <address@hidden> wrote:

> Il 11/09/2014 19:03, Chris Webb ha scritto:
>> Paolo Bonzini <address@hidden> wrote:
>> 
>>> This is a hypercall that should have kicked VCPU 3 (see rcx).
>>> 
>>> Can you please apply this patch and gather a trace of the host
>>> (using "trace-cmd -e kvm qemu-kvm <arguments>")?
>> 
>> Sure, no problem. I've built the trace-cmd tool against udis86 (I hope) and
>> have put the resulting trace.dat at
>> 
>>  http://cdw.me.uk/tmp/trace.dat
>> 
>> This is actually for a -smp 2 qemu (failing to kick VCPU 1?) as I was having
>> trouble persuading the -smp 4 qemu to crash as reliably under tracing.
>> (Something timing related?) Otherwise the qemu-system-x86 command line is
>> exactly as before.
> 
> Do you by chance have CONFIG_DEBUG_RODATA set?  In that case, the fix is
> simply not to set it.

Absolutely right: my host and guest kernels do have CONFIG_DEBUG_RODATA set!

Your patch to use alternatives for VMCALL vs VMMCALL definitely fixed the
divide-by-zero crashes I saw.

Given that I can easily use either (or both) of these solutions, is it be
more efficient to turn off CONFIG_DEBUG_RODATA in the guest kernel so kvm
can fix up the instructions in-place, or is using alternatives for
VMCALL/VMMCALL as implemented by your patch just as good?

Best wishes,

Chris.