Re: [Qemu-devel] issues of region cache and iommu reset

[Paolo Bonzini]

On 29/03/2017 11:09, Jason Wang wrote:
>>>>
>>> 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?
> 
> Yes.  In this case, virtio-net-pci is not reset, but vtd has been reset.
> So virtio-net-pci will still try to use the iova of ring to setup the
> cache but now vtd treat iova as gpa since dmar has been disabled during
> reset. (E.g In my test with Linux driver, desc map succeed but used fail.)

That would be a Linux bug, the devices below the IOMMU have to be reset
first.

Paolo