> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Friday, November 4, 2022 9:01 AM > > The only way I can see to solve this is to hold a serializing lock > across iommufd_access_pin_pages() so that neither > iommufd_test_access_unmap() can progress until both the pin is > completed and the record of the pin is stored. same as gvt does which maintains an internal mapping cache and conducts pin/unmap with cache update under the mutex protection. > > Fortunately in the iommufd design we can hold a lock like this across > these calls, and in the op callback, without deadlocking. I can't > recall if vfio can do the same, I suspect not since I had in my mind I > needed to avoid that kind of locking for deadlock reasons.. I think so. iiuc vfio relies on driver to ensure serialization in this scenario.
