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Caching qemu capabilities and KubeVirt
by Roman Mohr 13 Oct '22

13 Oct '22

Hi, I have a question regarding capability caching in the context of KubeVirt. Since we start in KubeVirt one libvirt instance per VM, libvirt has to re-discover on every VM start the qemu capabilities which leads to a 1-2s+ delay in startup. We already discover the features in a dedicated KubeVirt pod on each node. Therefore I tried to copy the capabilities over to see if that would work. It looks like in general it could work, but libvirt seems to detect a mismatch in the exposed KVM CPU ID in every pod. Therefore it invalidates the cache. The recreated capability cache looks esctly like the original one though ... The check responsible for the invalidation is this: ``` Outdated capabilities for '%s': host cpuid changed ``` So the KVM_GET_SUPPORTED_CPUID call seems to return slightly different values in different containers. After trying out the attached golang scripts in different containers, I could indeed see differences. I can however not really judge what the differences in these KVM function registers mean and I am curious if someone else knows. The files are attached too (as json for easy diffing). Best regards, Roman

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MemoryBacking options
by Simon Fairweather 10 Oct '22

10 Oct '22

Hi, Is there any documentation that states which options can be used together with each other. <domain> ... <memoryBacking> <hugepages> <page size="1" unit="G" nodeset="0-3,5"/> <page size="2" unit="M" nodeset="4"/> </hugepages> <nosharepages/> <locked/> <source type="file|anonymous|memfd"/> <access mode="shared|private"/> <allocation mode="immediate|ondemand" threads='8'/> <discard/> </memoryBacking> ... </domain>

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Re: Why host device disappear in libvirt doman xml?
by Michal Prívozník 29 Sep '22

29 Sep '22

[Once again, please keep the list on CC] On 9/29/22 04:59, 陈新隆 wrote: > Thanks for the detail explanation, it's very helpful. > > I guess : > 1. virsh dumpxml <domain> outputs the live xml(or active xml) Yes, if domain is running then it outputs the live XML, otherwise it outputs the inactive XML. For running domains you can use --inactive flag to get the inactive XML. > 2. virsh edit <domain> edits the inactive xml, so I should cold boot > domain to take effect Correct. Michal

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Re: Why host device disappear in libvirt doman xml?
by Michal Prívozník 28 Sep '22

28 Sep '22

[Please, keep the list on CC for benefit of others] On 9/28/22 10:13, 陈新隆 wrote: > I'm using the `virsh dumpxml <domain name>` to check the xml. When I > first execute this command, there's two hostdev(GPU) in the xml, but > next time I execute the same command these two hostdev elements > disappeared. During this time, the vm didn't restart or stop. Also, > within the vm `lspci | grep -i nvidia` command did not print GPU infos. > > So I was wondering if there's a mechanism in libvirtd detach the hostdev > element without the vm stop or restart. This problem doesn't happen > often, so I am looking a way to reproduce it. > > Can you help me with these questions : > > 1. If I edit the xml manually then detached the hostdev elements from > xml by invoke libvirtd apis, will the vm apply it immediately without > stop or restart? Or I must restart the vm to apply the latest xml ? I'm not sure what you mean. Editing XML manually is different to using libvirt APIs to detach hostdevs. Here's how it works: 1) a domain is defined (say using virsh define file.xml), libvirt parses this XML, keeps it in a memory and stores it "somewhere" (it's under /etc/libvirt/qemu/ but we do not want users to hand edit those files manually as libvirt reads them only on libvirtd/virtqemud restart). This is called inactive XML, because it reflects the inactive state of domain. Sometimes it's also called config XML. 2) when the domain is started (e.g. virsh start), libvirt creates a copy of inactive XML, populates it with runtime information and saves it elsewhere (/run/libvirt/qemu/, but again, we do not want users to hand edit those files). This copy is referred to as live XML. 3) users can alter the live XML using APIs (e.g. to hotplug a device or hotunplug it). The inactive XML can be altered by providing altered XML and defining it again (here, domain name and UUID must match already existing domain). 4) upon domain shutoff, the live XML is thrown away, and finally 5) the inactive XML is never thrown away, until virsh undefine is called. Now, you can see that there's no real connection between live and inactive XMLs and changing one has no affect on the other, except when the domain is cold booted again. Live and inactive XMLs can vary wildly. Therefore, you can have inactive XML with two <hostdev/>-s, and active XML with no <hostdev> at all. NB, hotplug APIs can also be used to alter inactive XML (virsh attach-device --config / virsh detach-device --config / ...) or both at the same time (virsh attach-device --config --live / virsh attach-device --config --live / ...). And what you describe sounds as if those two <hostdev/>-s you saw at domain startup were hotunplugged. The fact that even 'lspci' ran from inside the domain can't find them only supports this theory. And no, libvirt never tries to bring inactive and live XMLs together. It has no intelligence built in to do that and we, developers, do not want such thing either. We might change something that user specifically wanted and I believe nobody likes those "smart" tools that get in your way. > 2. After a host device is hot-unplugged, will libvirtd aware of it then > remove the related `hostdev` element from xml ? Yes. I believe the reasoning is seen in the previous block of my reply. > > On Mon, Sep 26, 2022 at 10:10 PM Michal Prívozník <mprivozn(a)redhat.com > <mailto:mprivozn@redhat.com>> wrote: > > On 9/26/22 15:06, 陈新隆 wrote: > > > > <https://stackoverflow.com/posts/73854544/timeline > <https://stackoverflow.com/posts/73854544/timeline>> > > > > I'm using Kubevirt to manage my virtual machine instances. When I > using > > Kubevirt to create a vm(with two GPUs), kubevirt will generate a > libvirt > > guest domain xml for this vm which includes two GPUs, the domain > xml as > > follow : > > > > |<hostdev mode='subsystem' type='pci' managed='no'> <driver > > name='vfio'/> <source> <address domain='0x0000' bus='0x83' slot='0x00' > > function='0x0'/> </source> <alias name='ua-gpu-gpu0'/> <address > > type='pci' domain='0x0000' bus='0x06' slot='0x00' function='0x0'/> > > </hostdev> <hostdev mode='subsystem' type='pci' managed='no'> <driver > > name='vfio'/> <source> <address domain='0x0000' bus='0x84' slot='0x00' > > function='0x0'/> </source> <alias name='ua-gpu-gpu1'/> <address > > type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/> > > </hostdev> | > > > > No one ever edit this domain xml, but these two |hostdev| element > > disappeared in the domain xml. During this time, I've run > > the |gpu_burn| command to do a stress test for these two GPUs. > > > > My question is : > > > > * when will libvirtd change the guest domain xml ? > > * why libvirtd delete these two |hostdev| from domain xml ? > > > > Libvirt does not remove anything from domain XML (except for the > elements it does not understand, but this is not the case). My suspicion > is that you're looking at live XML instead of inactive XML or vice > versa. Libvirt allows guests to be defined (i.e. libvirt manages their > inactive definition). However, a guest can be started with wildly > different configuration (e.g. without those two <hostdev/>-s). OR, they > might have been hot-unplugged. > > I still recommend reading this link: > This article can explain more details: > https://wiki.libvirt.org/page/VM_lifecycle > <https://wiki.libvirt.org/page/VM_lifecycle> Michal

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[Question] Should libvirt update live xml accordingly when guest mac is changed?
by Fangge Jin 26 Sep '22

26 Sep '22

Hi I met an issue when testing trustGuestRxFilters: Attach a macvtap interface with trustGuestRxFilters=’yes’ to vm, then change interface mac address in vm. Should libvirt update interface mac in live vm xml accordingly? If not, vm network will be broken after managedsaving and restoring vm. BR, Fangge Jin Steps: 1. Start a vm 2. Attach a macvtap interface with trustGuestRxFilters=’yes’ to vm <interface type='direct' trustGuestRxFilters='yes'> <source dev='enp175s0v0' mode='passthrough'/> <target dev='macvtap0'/> <model type='virtio'/> <alias name='net1'/> </interface> 3. Check vm xml: # virsh dumpxml uefi --xpath //interface <interface type="direct" trustGuestRxFilters="yes"> <mac address="52:54:00:46:88:8b"/> <source dev="enp175s0v0" mode="passthrough"/> <target dev="macvtap2"/> <model type="virtio"/> <alias name="net0"/> <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/> </interface> 4. Change interface mac in guest: # ip link set dev enp1s0 address 52:54:00:9d:a1:1e # ip a 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 4: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 52:54:00:9d:a1:1e brd ff:ff:ff:ff:ff:ff permaddr 52:54:00:46:88:8b inet 192.168.124.5/24 scope global enp1s0 valid_lft forever preferred_lft forever # ping 192.168.124.4 PING 192.168.124.4 (192.168.124.4) 56(84) bytes of data. 64 bytes from 192.168.124.4: icmp_seq=1 ttl=64 time=0.240 ms 64 bytes from 192.168.124.4: icmp_seq=2 ttl=64 time=0.138 ms --- 192.168.124.4 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1001ms 5. Check vm xml: # virsh dumpxml uefi --xpath //interface <interface type="direct" trustGuestRxFilters="yes"> <mac address="52:54:00:46:88:8b"/> <source dev="enp175s0v0" mode="passthrough"/> <target dev="macvtap2"/> <model type="virtio"/> <alias name="net0"/> <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/> </interface> 6. Check on host: 16: macvtap1@enp175s0v0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 500 link/ether 52:54:00:9d:a1:1e brd ff:ff:ff:ff:ff:ff inet6 fe80::5054:ff:fe46:888b/64 scope link valid_lft forever preferred_lft forever 7. Do managedsave and restore # virsh managedsave uefi Domain 'uefi' state saved by libvirt # virsh start uefi Domain 'uefi' started 8. Check vm network function: # ip a 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 4: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 52:54:00:9d:a1:1e brd ff:ff:ff:ff:ff:ff permaddr 52:54:00:46:88:8b inet 192.168.124.5/24 scope global enp1s0 valid_lft forever preferred_lft forever # ping 192.168.124.4 PING 192.168.124.4 (192.168.124.4) 56(84) bytes of data. --- 192.168.124.4 ping statistics --- 3 packets transmitted, 0 received, 100% packet loss, time 2036ms

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Why host device disappear in libvirt doman xml?
by 陈新隆 26 Sep '22

26 Sep '22

<https://stackoverflow.com/posts/73854544/timeline> I'm using Kubevirt to manage my virtual machine instances. When I using Kubevirt to create a vm(with two GPUs), kubevirt will generate a libvirt guest domain xml for this vm which includes two GPUs, the domain xml as follow : <hostdev mode='subsystem' type='pci' managed='no'> <driver name='vfio'/> <source> <address domain='0x0000' bus='0x83' slot='0x00' function='0x0'/> </source> <alias name='ua-gpu-gpu0'/> <address type='pci' domain='0x0000' bus='0x06' slot='0x00' function='0x0'/> </hostdev> <hostdev mode='subsystem' type='pci' managed='no'> <driver name='vfio'/> <source> <address domain='0x0000' bus='0x84' slot='0x00' function='0x0'/> </source> <alias name='ua-gpu-gpu1'/> <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/> </hostdev> No one ever edit this domain xml, but these two hostdev element disappeared in the domain xml. During this time, I've run the gpu_burn command to do a stress test for these two GPUs. My question is : - when will libvirtd change the guest domain xml ? - why libvirtd delete these two hostdev from domain xml ?

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Backup KVM Guest VM in OVA or VMDK format
by Kaushal Shriyan 22 Sep '22

22 Sep '22

Hi, Is there a way to backup KVM Guest VM in kvmguestosimage.ova or kvmguestosimage.vmdk format as I am trying to restore it in AWS by referring to https://aws.amazon.com/ec2/vm-import/ article as per the below supported file format. [1] Open Virtualization Archive (OVA) [2] Virtual Machine Disk (VMDK) [3] Virtual Hard Disk (VHD/VHDX) [4] raw Also any method to take full and incremental backup of KVM Guest VM. Any help will be highly appreciated. I look forward to hearing from you. Thanks in Advance. Best Regards, Kaushal

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How can I check the history of all console logs starting from the first second of bootup
by Lucas Liu 22 Sep '22

22 Sep '22

Gratings: Recently, I got an error while installing a guest, the error message is this,: [image: image.png] Is there a method to get the full log? I have tried to use virt-install --console, or attach <log file="/var/log/libvirt/qemu/guestname-serial0.log" append="off"/> to get the full log, but they didn't work.

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Re: Help in porting smack related patches to meson build system
by Peter Krempa 20 Sep '22

20 Sep '22

On Mon, Sep 19, 2022 at 16:31:25 +0000, Vishal Gupta (vishagu2) wrote: > Hi Peter , Hi, I firstly want to ask you to avoid top-posting on technical mailing lists. > > > > Thanks for ur reply . > > > > Kirkstone is the latest release from Yocto foundation . details https://docs.yoctoproject.org/dev/migration-guides/migration-4.0.html > > > > Kirkstone support libvirt 8.10 https://layers.openembedded.org/layerindex/recipe/3052/ > > > > We are trying to port 2016 smack patch " https://listman.redhat.com/archives/libvir-list/2016-July/msg00456.html" for libvirt which is based on automake make file Okay so that is quite an old patch which was never finished and merged. > But above patch is incompatible with libvirt 8.10 .as libvirt 8.1 supports only meson > > > I was just wondering if above smack patch is already ported for meson based libvirt 8.10? > > We have issue in porting m4/virt-smack.m4 to meson.build file . virt-smack.m4 is define in 2016 smack patch No it is not ported. I want to warn you though that porting the build system part to meson will not be biggest of the problems. 1) The patch is more than 6 years old at this point There's quite a lot of change in libvirt during that time. Many helpers and internal APIs were refactored. The patch even once you port the build system will require *significant* rework to actually even compile. 2) libsmack (smack-utils) used by the new security module is not present in distros The library it requires doesn't seem to be adopted much: https://repology.org/project/smack-utils/versions Did you make sure that it's present in your environment? Additionally if you want to get the patch accepted upstream note that there were outstanding problems with the patch in the last version which is on the mailing list. I can see that there are definitely problems with coding style and the patch will need to be split to logical chunks as it's now just a big blob of code. Also given that the library is simply not present in distros it will require a justification why upstream should cary the patch. Carying code which is not compiled because of lack of dependencies is a burden to upstream and still can bitrot in the future. Even if you are not striving for upstreaming the patch, be prepared for more work than just porting the build system.

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Help in porting smack related patches to meson build system
by Akash Bhaskaran (akabhask) 19 Sep '22

19 Sep '22

Hi, We are trying to port some patches pertaining to files like Makefile.am ,configure.ac and .m4’s to libvirt kirkstone release. We see that latest kirskstone now uses meson build architecture. We have difficulties in porting the changes in the above-mentioned files to meson. Is there any script or reference you can provide for helping us port these files to meson? Thanks, Akash

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