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setting bridge for VMs IP assignment by router's DHCP server
by Germano Massullo 03 Aug '24

03 Aug '24

I am running a libvirt hostmachine (Fedora 40) which has 192.168.1.6 IP address, assigned by router's DHCP server. I want the libvirt VMs IPs to be assigned by router's DHCP server, so I tried to setup a bridge via # virsh net-define foo.xml and trying the following files as xml file, but they all failed to achieve the task. Here I list the two XML variants I tried to use 1) <network> <name>bridge-no-nat</name> <bridge name='virbr1_no-nat' stp='on' delay='0'/> <forward mode='open'/> </network> RETURNS: open forwarding requested, but no IP address provided for network 'bridge-no-nat' 2) I created in nmtui the bridge virbr1_no_nat then I used following XML for virsh net-define <network> <name>br1_no_nat</name> <forward mode='bridge'/> <bridge name='virbr1_no_nat'/> <virtualport type='openvswitch'/> <portgroup name='default'/> </network> then I configure the VM network to use but when I start the VM I get error: internal error: Unable to add port vnet1 to OVS bridge virbr1_no_nat: <null> Do you know how I can solve this? Thank you

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KVM static internal networking without host bridge interface (virbr)
by Daniel 02 Aug '24

02 Aug '24

How to set up an internal network between two KVM network interfaces while using static networking (avoiding dnsmasq) and while avoiding a host bridge interface (virbr)? Currently I am using this for the network. <network> <name>Internal</name> <bridge name='virbr2' stp='on' delay='0'/> </network> And then for the VM. <interface type='network'> <source network='Internal'/> <model type='virtio'/> <driver name='qemu'/> </interface> * I would like to avoid the host `virbr2` interface. This is because ideally package sniffers on the host such as tshark / wireshark would be unable to see these packages following between an internal network between two VMs. * SLIRP should be avoided due to past security issues. [1] * dnsmasq on the host operating system or inside the VMs should also be avoided in favor of static IP addresses. By comparison, this is possible in VirtualBox. [2] Is that possible with KVM too? Could you please show an example configuration file on how to accomplish that? [1] CVE-2019-6778 [2] VirtualBox has this capability. VirtualBox can have an internal network using static networking. No vibr bridge interfaces can be seen on the host operating system. And VM to VM internal traffic is not visible to package analyzers on the host operating system either. Regards, Daniel -- Daniel Winzen Steinkaulstr. 47 52070 Aachen Germany Web: https://danwin1210.de/ E-Mail: daniel(a)danwin1210.de Phone: +49 176 98819809 PGP-Key: https://danwin1210.de/pgp.txt

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Certificate verification error for qemu while migrating
by jdeberles＠gmail.com 29 Jul '24

29 Jul '24

Hello, I'm running ovirt 4.4.10 (using libvirt 7.10.0-1.module_el8.6.0+1046+bd8eec5e) and I have the following qemu error while I launch a VM migration Jul 3 12:37:07myhostname1 journal[958949]: Certificate [session] owner does not match the hostname myhostname2 Jul 3 12:37:07 myhostname1journal[958949]: Certificate check failed Certificate [session] owner does not match the hostname myhostname2 Jul 3 12:37:07 myhostname1 journal[958949]: authentication failed: Failed to verify peer's certificate Jul 3 12:37:07myhostname1 journal[958949]: operation failed: Failed to connect to remote libvirt URI qemu+tls://myhostname3/system: authentication failed: Failed to verify peer's certificate To avoid this error I set the following paramaters inside the /etc/libvirt/qemu.conf and restard vdsmd and libvirtd daemons. migrate_tls_x509_verify = 0 default_tls_x509_verify = 0 But I still have the same error. Can you help me to understand why this set of parameters are not working as expected ? kind regards, Julien

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can this network setup works?
by daggs 13 Jul '24

13 Jul '24

Greetings, I have this setup. host and two vms, a and b. vm a servers as router, it has one physical nic passed directly into it. I want to connect vm a to vm b and the host to provide internet access to both. so I've created a virtual switch like this: <network> <name>default</name> <uuid>f90b3044-81c1-4c22-98df-8bbca3153f21</uuid> <bridge name='virsw0' stp='on' delay='0'/> <mac address='52:54:00:6b:1b:92'/> </network> with this xml entry: <interface type='bridge'> <mac address='xx:xx:xx:xx:xx:xx'/> <source bridge='virsw0'/> <model type='virtio'/> <address type='pci' domain='x' bus='x' slot='x' function='x'/> </interface> in vm a and vm b should connect the both to the virtual switch thus allowing vm b internet access. this however doesn't solves the host connection to the internet. reading docs points to the fact I can add new tun devs outside of libvirt and add it to the virtual switch. so I did this: $ ip tuntap add QemuTap0 mode tap user root $ ip link set QemuTap0 master virsw0 and brctl show virsw0 returns this: $ brctl show virsw0 bridge name bridge id STP enabled interfaces virsw0 8000.5254006b1b92 yes QemuTap0 so theoretically speaking, when vm a is started and libvirt creates a device and connects it to the virtual switch and run dhcpd, vm a will provide ip. am I correct? Thanks, Dagg

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per user vm isolation with shared network
by daggs 02 Jul '24

02 Jul '24

Greetings, I have two vm which I want to isolate per user, if I'm not mistaken, I can to that with per session uri. but I want to setup a virtual bridge so they will get connected with each other. looks like that if I define the network as system, it isn't visible in the session. is there a way to do that? if I define the same network in both sessions, will it work? Thanks, Dagg

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Re: dm-crypt performance regression due to workqueue changes
by Mikulas Patocka 02 Jul '24

02 Jul '24

On Sun, 30 Jun 2024, Tejun Heo wrote: > Hello, > > On Sat, Jun 29, 2024 at 08:15:56PM +0200, Mikulas Patocka wrote: > > > With 6.5, we get 3600MiB/s; with 6.6 we get 1400MiB/s. > > > > The reason is that virt-manager by default sets up a topology where we > > have 16 sockets, 1 core per socket, 1 thread per core. And that workqueue > > patch avoids moving work items across sockets, so it processes all > > encryption work only on one virtual CPU. > > > > The performance degradation may be fixed with "echo 'system' > > >/sys/module/workqueue/parameters/default_affinity_scope" - but it is > > regression anyway, as many users don't know about this option. > > > > How should we fix it? There are several options: > > 1. revert back to 'numa' affinity > > 2. revert to 'numa' affinity only if we are in a virtual machine > > 3. hack dm-crypt to set the 'numa' affinity for the affected workqueues > > 4. any other solution? > > Do you happen to know why libvirt is doing that? There are many other > implications to configuring the system that way and I don't think we want to > design kernel behaviors to suit topology information fed to VMs which can be > arbitrary. > > Thanks. I don't know why. I added users(a)lists.libvirt.org to the CC. How should libvirt properly advertise "we have 16 threads that are dynamically scheduled by the host kernel, so the latencies between them are changing and unpredictable"? Mikulas

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Command line equivalent for cpu pinning
by Gianluca Cecchi 28 Jun '24

28 Jun '24

Hello, on my Fedora 39 with libvirt 9.7.0-3.fc39 qemu-kvm 8.1.3-5.fc39 kernel 6.8.11-200.fc39.x86_64 I'm testing cpu pinning The hw is a Nuc with 13th Gen Intel(R) Core(TM) i7-1360P If I pass from this in my guest xml: <vcpu placement='static'>4</vcpu> <cpu mode='host-passthrough' check='none' migratable='on'> <topology sockets='1' dies='1' cores='4' threads='1'/> </cpu> to this: <vcpu placement='static'>4</vcpu> <cputune> <vcpupin vcpu='0' cpuset='0'/> <vcpupin vcpu='1' cpuset='2'/> <vcpupin vcpu='2' cpuset='4'/> <vcpupin vcpu='3' cpuset='6'/> </cputune> <cpu mode='host-passthrough' check='none' migratable='on'> <topology sockets='1' dies='1' cores='4' threads='1'/> </cpu> It seems to me that the generated command line of the qemu-system-x88_64 process doesn't change. As if the cputune options were not considered What should I see as different? Actually it seems it is indeed honored, because if I run stress-ng in the VM in the second scenario and top command in the host, I see only pcpu 0,2,4,6 going up with the load. Instead the first scenario keeps several different cpus alternating in the load. The real question could be: if I want to reproduce from the command line the cputune options, how can I do it? Is it only a cpuset wrapper used for the qemu-system-x86_64 process to place it in a cpuset control group? I see for the pid of the process $ sudo cat /proc/340215/cgroup 0::/machine.slice/machine-qemu\x2d8\x2dc7anstgt.scope/libvirt/emulator and $ sudo systemd-cgls /machine.slice CGroup /machine.slice: └─machine-qemu\x2d8\x2dc7anstgt.scope … └─libvirt ├─340215 /usr/bin/qemu-system-x86_64.... ├─vcpu1 ├─vcpu2 ├─vcpu0 ├─emulator └─vcpu3 What could be an easy command to replicate from the command line what virsh does? Thanks in advance Gianluca

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cpu vmx migration issue
by d tbsky 25 Jun '24

25 Jun '24

Hi: I update our RHEL9 system to RHEL 9.4, which brings libvirt 10.0. I try to calculate the cpu baseline for our two-node cluster with command "virsh domcapabilities" then "virsh hypervisor-cpu-baseline --migratable". the result has many cpu features begin with "vmx". the test cluster has cpu "intel E3-1280 V3" and "intel I3-9100F". when I try live migrate vm, it failed and told me "guest CPU doesn't match specification: missing features: vmx-apicv-register,vmx-apicv-vid,vmx-posted-intr". at another cluster with cpu " Intel i5-2520M" and "Intel i7-9750H" the migration works fine for the calculated cpu result. although there are still many "vmx" cpu features in the result. if I delete all these vmx features, then migration works fine for both cluster, like old days. I wonder what's the benefit to expose these vmx features to guest if I don't do any nested virtualization. is it ok the drop all these vmx cpu features for a guest? thanks a lot for help!

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unable to start a nested vm due to iommu_group issue
by daggs 22 Jun '24

22 Jun '24

Greetings, I'm working on a new os for my server which runs 2 vms. I'm using nested vms to work on it so I won't take down the server. the new os is alpine 3.20, qemu is 9.0.1, libvirt is 10.3.0. I have a device I want to pass to one of the guests, here is the iommu group layout: IOMMU Group 18 00:1f.0 ISA bridge [0601]: Intel Corporation 82801IB (ICH9) LPC Interface Controller [8086:2918] (rev 02) IOMMU Group 18 00:1f.2 SATA controller [0106]: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA Controller [AHCI mode] [8086:2922] (rev 02) IOMMU Group 18 00:1f.3 SMBus [0c05]: Intel Corporation 82801I (ICH9 Family) SMBus Controller [8086:2930] (rev 02) IOMMU Group 18 00:1f.4 Audio device [0403]: Intel Corporation 82801I (ICH9 Family) HD Audio Controller [8086:293e] (rev 03) the device in question is 00:1f.4: utils-server:/home/igor# lspci -s 00:1f.4 -nnv 00:1f.4 Audio device [0403]: Intel Corporation 82801I (ICH9 Family) HD Audio Controller [8086:293e] (rev 03) Subsystem: Red Hat, Inc. QEMU Virtual Machine [1af4:1100] Flags: bus master, fast devsel, latency 0, IRQ 10, IOMMU group 18 Memory at e1080000 (32-bit, non-prefetchable) [size=16K] Capabilities: [60] MSI: Enable- Count=1/1 Maskable- 64bit+ Kernel driver in use: vfio-pci to achieve that, I've compiled the kernel with acs patch and defined it in the kernel cmdline: BOOT_IMAGE=/boot/vmlinuz-lts root=UUID=44299ace-27c6-4047-8cbd-bbffcc0a65f0 ro modules=sd-mod,usb-storage,ext4 quiet rootfstype=ext4 iommu=pt intel_iommu=on pcie_acs_override=id:8086:293e,8086:10c9 I see in dmesg, acs is enabled, see: # dmesg | grep "ACS overrides" [ 0.000000] Warning: PCIe ACS overrides enabled; This may allow non-IOMMU protected peer-to-peer DMA the xml file can be found at https://bpa.st/FARQ. when I try to start the vm, I get this: # virsh start streamer error: Failed to start domain 'streamer' error: internal error: QEMU unexpectedly closed the monitor (vm='streamer'): 2024-06-21T08:39:17.959476Z qemu-system-x86_64: -device {"driver":"vfio-pci","host":"0000:00:1f.4","id":"hostdev0","bus":"pcie.0","addr":"0x1f.0x5"}: vfio 0000:00:1f.4: group 18 is not viable Please ensure all devices within the iommu_group are bound to their vfio bus driver any ideas what am I missing? is it possible this cannot work within a vm? Thanks, Dagg

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librbd encryption and guest XML
by melanie witt 18 Jun '24

18 Jun '24

Hi, I have been trying to use the librbd engine to run a guest from an encrypted RBD image and am running into some problems. What I would like to do is: 1. Start from an unencrypted raw image with an OS 2. Make an encrypted clone of that image 3. Boot a guest from the encrypted clone image What I have tried so far (simplified): 1. Make a clone of the unencrypted image rbd clone images/unencrypted@snap images/encryptedclone 2. Format the clone image with encryption rbd encryption format images/encryptedclone luks1 passphrase.bin 3. Create guest XML with the encrypted clone [...] <disk type="network" device="disk"> <driver type="raw" cache="writeback"/> <source protocol="rbd" name="images/encryptedclone"> <host name="127.0.0.1" port="6789"/> <encryption format="luks" engine="librbd"> <secret type="passphrase" uuid="secretuuid"/> </encryption> </source> <auth username="cinder"> <secret type="ceph" uuid="othersecretuuid"/> </auth> <target dev="vda" bus="virtio"/> </disk> [...] and virDomainCreateWithFlags() with the XML. I don't get any errors from libvirt (no errors about loading encryption) but this configuration does not seem to work, the guest won't boot. If anyone can give me a hint what I'm doing wrong, I would appreciate it. Cheers, -melwitt

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