Description of problem: When a VM contains a PCI host devices and its maximum number of vCPUs is at least 256 then the VM fails to start. Version-Release number of selected component (if applicable): 4.4.9 How reproducible: 100% Steps to Reproduce: 1. Add a PCI host device (for example a sound card) to a VM with many vCPUs (e.g. a Q35 VM with 1 socket, 16 cores, 1 thread CPU topology). 2. Try to start the VM. Actual results: The VM fails to start with the following error: qemu-kvm: We need to set caching-mode=on for intel-iommu to enable device assignment with IOMMU protection. Expected results: The VM starts. Additional info: This is basically the same as BZ 2013752, which handled only VMs with vGPU, while the same problem applies also to VMs with any vfio-pci device.
oops, targeted to 4.4.10
*** Bug 2026893 has been marked as a duplicate of this bug. ***
Verified: ovirt-engine-4.5.0-0.237.el8ev vdsm-4.50.0.10-1.el8ev.x86_64 qemu-kvm-6.2.0-10.module+el8.6.0+14540+5dcf03db.x86_64 libvirt-daemon-8.0.0-5.module+el8.6.0+14480+c0a3aa0f.x86_64 Verification scenario: 1. Create VM with mdev and VFIO (USB passthrough in this case) with 16 total virtual CPUs (1 socket and 16 cores per socket) 2. Run VM and verify VM is running. 3. Observe VM xml and verify caching=on: <iommu model="intel"> <driver caching_mode="on" eim="on" intremap="on" /> </iommu> 4. Repeat steps 1-3, this time use 24 CPus and 32 CPUs.
This bugzilla is included in oVirt 4.5.0 release, published on April 20th 2022. Since the problem described in this bug report should be resolved in oVirt 4.5.0 release, it has been closed with a resolution of CURRENT RELEASE. If the solution does not work for you, please open a new bug report.