> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx> > Sent: Thursday, August 31, 2023 5:28 PM > > On 2023/8/30 15:43, Tian, Kevin wrote: > >> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx> > >> Sent: Saturday, August 26, 2023 4:01 PM > >> > >> On 8/25/23 4:17 PM, Tian, Kevin wrote: > >>>> + > >>>> /** > >>>> * iopf_queue_flush_dev - Ensure that all queued faults have been > >>>> processed > >>>> * @dev: the endpoint whose faults need to be flushed. > >>> Presumably we also need a flush callback per domain given now > >>> the use of workqueue is optional then flush_workqueue() might > >>> not be sufficient. > >>> > >> > >> The iopf_queue_flush_dev() function flushes all pending faults from the > >> IOMMU queue for a specific device. It has no means to flush fault queues > >> out of iommu core. > >> > >> The iopf_queue_flush_dev() function is typically called when a domain is > >> detaching from a PASID. Hence it's necessary to flush the pending faults > >> from top to bottom. For example, iommufd should flush pending faults in > >> its fault queues after detaching the domain from the pasid. > >> > > > > Is there an ordering problem? The last step of intel_svm_drain_prq() > > in the detaching path issues a set of descriptors to drain page requests > > and responses in hardware. It cannot complete if not all software queues > > are drained and it's counter-intuitive to drain a software queue after > > the hardware draining has already been completed. > > > > btw just flushing requests is probably insufficient in iommufd case since > > the responses are received asynchronously. It requires an interface to > > drain both requests and responses (presumably with timeouts in case > > of a malicious guest which never responds) in the detach path. > > You are right. Good catch. > > To put it simply, iopf_queue_flush_dev() is insufficient to support the > case of forwarding iopf's over iommufd. Do I understand it right? yes > > Perhaps we should drain the partial list and the response pending list? > With these two lists drained, no more iopf's for the specific pasid will > be forwarded up, and page response from upper layer will be dropped. > correct.
