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