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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Wed, 29 Mar 2017 10:41:56 +0200
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Subject: Re: [Qemu-devel] issues of region cache and iommu reset
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To: Jason Wang <jasowang@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: Peter Xu <peterx@redhat.com>, qemu devel <qemu-devel@nongnu.org>, Cornelia Huck <cornelia.huck@de.ibm.com>



On 29/03/2017 10:37, Jason Wang wrote:
>>
>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>> index 03592c5..73e69ac 100644
>> --- a/hw/virtio/virtio.c
>> +++ b/hw/virtio/virtio.c
>> @@ -176,6 +176,10 @@ err_used:
>>       address_space_cache_destroy(&new->desc);
>>   err_desc:
>>       g_free(new);
>> +    atomic_rcu_set(&vq->vring.caches, NULL);
>> +    if (old) {
>> +        call_rcu(old, virtio_free_region_cache, rcu);
>> +    }
>>   }
>>
>>   /* virt queue functions */
>>
>> Paolo
> 
> This looks a good fix but may not solve this issue completely. Depends
> on the iova that guest uses, address_space_cache_init() may succeed even
> in this case since vtd does a passthrough translation in this case.

Can you explain this more?

Paolo