[RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier

[Jason Wang]

On 2020/7/8 上午3:54, Peter Xu wrote:
> On Tue, Jul 07, 2020 at 04:03:10PM +0800, Jason Wang wrote:
>> On 2020/7/3 下午9:03, Peter Xu wrote:
>>> On Fri, Jul 03, 2020 at 03:24:19PM +0800, Jason Wang wrote:
>>>> On 2020/7/2 下午11:45, Peter Xu wrote:
>>>>> On Thu, Jul 02, 2020 at 11:01:54AM +0800, Jason Wang wrote:
>>>>>> So I think we agree that a new notifier is needed?
>>>>> Good to me, or a new flag should be easier (IOMMU_NOTIFIER_DEV_IOTLB)?
>>>> That should work but I wonder something as following is better.
>>>>
>>>> Instead of introducing new flags, how about carry the type of event in the
>>>> notifier then the device (vhost) can choose the message it want to process
>>>> like:
>>>>
>>>> static vhost_iommu_event(IOMMUNotifier *n, IOMMUTLBEvent *event)
>>>>
>>>> {
>>>>
>>>> switch (event->type) {
>>>>
>>>> case IOMMU_MAP:
>>>> case IOMMU_UNMAP:
>>>> case IOMMU_DEV_IOTLB_UNMAP:
>>>> ...
>>>>
>>>> }
>>> Looks ok to me, though imo we should still keep the registration information,
>>> so VT-d knows which notifiers is interested in which events.  E.g., we can
>>> still do something like vtd_as_has_map_notifier().
>>
>> Is this for a better performance?
>>
>> I wonder whether it's worth since we can't not have both vhost and vtd to be
>> registered into the same as.
> /me failed to follow this sentence.. :(


Sorry, I meant "vfio" instead "vtd".


>
>> So it should be functional equivalent to vtd_as_has_notifier().
> For example: in vtd_iommu_replay() we'll skip the replay if vhost has
> registered the iommu notifier because vtd_as_has_map_notifier() will return
> false.


Two questions:

- Do we care the performance here? If not, vhost may just ignore the MAP 
event?
- If we care the performance, it's better to implement the MAP event for 
vhost, otherwise it could be a lot of IOTLB miss

Thanks


>    It'll only return true if the device is a vfio-pci device.
>
> Without vtd_as_has_map_notifier(), how could we do that?
>