Updated my Lab Pool. For the Test: @lmolina said: Reboot your VMs, starting with Linux VMs that use PCI passthrough (GPU, NVMe, NIC). The new HVM PIRQ default applies to every VM at its next boot. If you set platform:hvm-pirq on a VM yourself, that value is kept. Devices that worked before must still work, with similar performance and CPU usage. If one doesn't, check whether platform:hvm-pirq=true brings it back, and tell us. -> No such VM on my Lab Pool, not tested Run your usual Xen Orchestra backups (incremental with NBD, full) and a restore. Every NBD backup now goes through new code (tapdisk's NBD server, parallel requests), so they must complete, and shouldn't get slower. -> ran a full backup job and an incremental backup job. No issues. No diffrences to previous backups. Watch the disk performance of your busiest VMs, on VHD and QCOW2 SRs. The locking change in tapdisk applies to every VM disk, not only QCOW2. -> Didn't notice any performance issues. After running the snapshot_fixer.py script if necessary, take, revert to and delete snapshots, including on VMs with several disks, and check that the VMs and their disks are as expected afterwards. The fix changes how xapi handles VDIs during reverts and SR scans. -> Performed test with 3 VMs, 1 with one disk, 2 with 2 discs. -> No issues seen.