I compiled and installed a kernel with https://github.com/torvalds/linux/blob/master/drivers/iommu/intel/iommu.c In this file I had to comment out: /* case IOMMU_CAP_DEFERRED_FLUSH: */ With this self compiled kernel the problem is not there. I guess that iommu.c patches in https://sources.debian.org/patches/linux/6.4.11-1/ cause the problems I discovered. How can I help further to solve the problem? What to do next?