Re: [PATCH 4/6] kvm-s390: Unlink vcpu on destroy

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Avi Kivity wrote:
> ehrhardt@linux.vnet.ibm.com wrote:
>> From: Carsten Otte <cotte@de.ibm.com>
>>
>> This patch makes sure we do unlink a vcpu's sie control block
>> from the system control area in kvm_arch_vcpu_destroy. This
>> prevents illegal accesses to the sie control block from other
>> virtual cpus after free.
>>
>> Reported-by: Mijo Safradin <mijo@linux.vnet.ibm.com>
>> Signed-off-by: Carsten Otte <cotte@de.ibm.com>
>> ---
>>  arch/s390/kvm/kvm-s390.c |    9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> Index: kvm/arch/s390/kvm/kvm-s390.c
>> ===================================================================
>> --- kvm.orig/arch/s390/kvm/kvm-s390.c
>> +++ kvm/arch/s390/kvm/kvm-s390.c
>> @@ -195,6 +195,9 @@ out_nokvm:
>>  void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>>  {
>>      VCPU_EVENT(vcpu, 3, "%s", "free cpu");
>> +    if (vcpu->kvm->arch.sca->cpu[vcpu->vcpu_id].sda ==
>> +        (__u64) vcpu->arch.sie_block)
>> +        vcpu->kvm->arch.sca->cpu[vcpu->vcpu_id].sda = 0;
>>      free_page((unsigned long)(vcpu->arch.sie_block));
>>
>>   
>
> If this is accessed by hardware on a different cpu, don't you need a 
> memory barrier here?
>
>
Right, will be in v2

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization