On 14/02/2018 17:44, Borislav Petkov wrote:
> On Thu, Feb 08, 2018 at 04:58:46PM -0600, Tom Lendacky wrote:
>> @@ -2681,11 +2731,15 @@ static int __msr_io(struct kvm_vcpu *vcpu, struct 
>> kvm_msrs *msrs,
>>  {
>>      int i, idx;
>>  
>> -    idx = srcu_read_lock(&vcpu->kvm->srcu);
>> +    if (vcpu)
>> +            idx = srcu_read_lock(&vcpu->kvm->srcu);
>> +
>>      for (i = 0; i < msrs->nmsrs; ++i)
>>              if (do_msr(vcpu, entries[i].index, &entries[i].data))
>>                      break;
>> -    srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> +
>> +    if (vcpu)
>> +            srcu_read_unlock(&vcpu->kvm->srcu, idx);
> 
> 
> ./include/linux/srcu.h:175:2: warning: ‘idx’ may be used uninitialized in 
> this function [-Wmaybe-uninitialized]
>   __srcu_read_unlock(sp, idx);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/x86/kvm/x86.c:2739:9: note: ‘idx’ was declared here
>   int i, idx;
>          ^~~
> 
> I know, silly gcc.
> 

Nice point---even better, just push srcu_read_lock/unlock to msr_io or
even msr_io's callers.

Thanks,

Paolo

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