Re: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb descriptor

[Jason Wang <jasowang@redhat.com>]

On 2017年02月16日 13:43, Jason Wang wrote:
>
>
> On 2017年02月16日 13:36, Liu, Yi L wrote:
>>> -----Original Message-----
>>> From: Qemu-devel 
>>> [mailto:qemu-devel-bounces+yi.l.liu=intel.com@nongnu.org]
>>> On Behalf Of Michael S. Tsirkin
>>> Sent: Tuesday, January 10, 2017 1:40 PM
>>> To: qemu-devel@nongnu.org
>>> Cc: Peter Maydell <peter.maydell@linaro.org>; Eduardo Habkost
>>> <ehabkost@redhat.com>; Jason Wang <jasowang@redhat.com>; Peter Xu
>>> <peterx@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Richard
>>> Henderson <rth@twiddle.net>
>>> Subject: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb
>>> descriptor
>>>
>>> From: Jason Wang <jasowang@redhat.com>
>>>
>>> This patch enables device IOTLB support for intel iommu. The major 
>>> work is to
>>> implement QI device IOTLB descriptor processing and notify the 
>>> device through
>>> iommu notifier.
>>>
>> Hi Jason/Michael,
>>
>> Recently Peter Xu's patch also touched intel-iommu emulation. His 
>> patch shadows
>> second-level page table by capturing iotlb flush from guest. It would 
>> result in page
>> table updating in host. Does this patch also use the same map/umap 
>> API provided
>> by VFIO?
>
> Yes, it depends on the iommu notifier too.
>
>> If it is, then I think it would also update page table in host. It 
>> looks to be
>> a duplicate update. Pls refer to the following snapshot captured from 
>> section 6.5.2.5
>> of vtd spec.
>>
>> "Since translation requests from a device may be serviced by hardware 
>> from the IOTLB, software must
>> always request IOTLB invalidation (iotlb_inv_dsc) before requesting 
>> corresponding Device-TLB
>> (dev_tlb_inv_dsc) invalidation."
>>
>> Maybe for device-iotlb, we need a separate API which just pass down 
>> the invalidate
>> info without updating page table. Any thoughts?
>
> cc Alex.
>
> If we want ATS to be visible for guest (but I'm not sure if VFIO 
> support this), we probably need another notifier or a new flag.
>
> Thanks 

Or need a dedicated address_space if ATS were enabled for the device.