On 18.12.2012, at 23:54, Scott Wood wrote:

> On 12/18/2012 06:38:41 AM, Alexander Graf wrote:
>> When we hit an emulation result that we didn't expect, that is an error,
>> but it's nothing that warrants a BUG(), because it can be guest triggered.
>> So instead, let's only WARN() the user that this happened.
>> Signed-off-by: Alexander Graf <ag...@suse.de>
>> ---
>> arch/powerpc/kvm/powerpc.c |    3 ++-
>> 1 files changed, 2 insertions(+), 1 deletions(-)
>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> index be83fca..e2225e5 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -237,7 +237,8 @@ int kvmppc_emulate_mmio(struct kvm_run *run, struct 
>> kvm_vcpu *vcpu)
>>              r = RESUME_HOST;
>>              break;
>>      default:
>> -            BUG();
>> +            WARN_ON(1);
>> +            r = RESUME_GUEST;
> 
> Do you have a specific way of a guest triggering this in mind, or is it just 
> being cautious?  The guest probably shouldn't be allowed to spam the kernel 
> log with WARNs either.  Is a traceback even useful here?

For debugging, yes. But maybe we would be better off with a trace point. 
Anyway, a WARN is better than a BUG either way for now.

I was able to provoke this by live patching an instruction without flushing the 
icache, so that the last_inst instruction fetch gets a different instruction 
from the instruction that resulted in the trap we're currently in.


Alex

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