Hugepages -- "Memory backend 'pc.ram' not found"
Charles Polisher
chas at chasmo.org
Tue Feb 22 22:02:00 UTC 2022
On 2/22/22 00:25, Michal Prívozník wrote:
> On 2/21/22 17:12, Charles Polisher wrote:
>
> Hey, please the list on CC for benefit of others, e.g. when somebody
> runs into the same problem they can find the discussion in the archive.
Oops... unintentional.
>> On 2/21/22 01:54, Michal Prívozník wrote:
>>> On 2/20/22 04:07, Charles Polisher wrote:
>>>> Hello,
>>>>
>>>> After defining hugepages, as documented at
>>>> https://libvirt.org/formatdomain.html#memory-backing ,
>>>> when I start the guest, I get a dialogue
>>>> box that says:
>>>>
>>>> Error starting domain: internal error: qemu unexpectedly
>>>> closed the monitor: 2022-02-20T01:10:36.520955Z
>>>> qemu-system-x86_64: Memory backend 'pc.ram' not found
>>>> Traceback (most recent call last):
>>>> File "/usr/share/virt-manager/virtManager/asyncjob.py", line 65,
>>>> in cb_wrapper
>>>> callback(asyncjob, *args, **kwargs)
>>>> File "/usr/share/virt-manager/virtManager/asyncjob.py", line 101,
>>>> in tmpcb
>>>> callback(*args, **kwargs)
>>>> File
>>>> "/usr/share/virt-manager/virtManager/object/libvirtobject.py", line 57,
>>>> in newfn
>>>> ret = fn(self, *args, **kwargs)
>>>> File "/usr/share/virt-manager/virtManager/object/domain.py", line
>>>> 1329, in startup
>>>> self._backend.create()
>>>> File "/usr/lib64/python3.9/site-packages/libvirt.py", line 1353,
>>>> in create
>>>> raise libvirtError('virDomainCreate() failed'
>>>>
>>>> After backing out changes, guest starts normally.
>>>> I searched online for the error message, but found nothing useful.
>>>> The hypervisor is running libvirtd (libvirt) 7.8.0 and QEMU emulator
>>>> version 6.1.0,
>>>> both build from source. I've got plenty of hugepages available.
>>>> The domain's XML definition is attached.
>>> Hey, can you share your domain XML and the generated cmd line? The
>>> latter should be found in /var/log/libvirt/qemu/$domain.log
>>>
>>> Thanks,
>>> Michal
>> Thanks for your reply. As requested, the domain XML:
>>
>> <domain type="kvm">
>> <name>slacky-0</name>
>> <uuid>4a67eb39-9b92-8b8a-97ba-7e1250d56b07</uuid>
>> <title>slacky-0</title>
>> <description>elided</description>
>> <memory unit="KiB">4194304</memory>
>> <currentMemory unit="KiB">4194304</currentMemory>
>> <memoryBacking>
>> <hugepages>
>> <page size="4194304" unit="KiB"/>
>>
>> This does not look correct. This is on x86_64 and there is no such size
>> for hugepages, only 2MiB and 1GiB.
Interesting. I had originally specified a different page size
and units (probably GiB), but "virsh edit" rewrote the value
after I completed the edit, with the result above.
>> </hugepages>
>> </memoryBacking>
>> <vcpu placement="static">2</vcpu>
>> <os>
>> <type arch="x86_64" machine="pc-i440fx-5.1">hvm</type>
>> <bootmenu enable="no"/>
>> </os>
>> <features>
>> <acpi/>
>> <apic/>
>> <pae/>
>> </features>
>> <cpu mode="custom" match="exact" check="none">
>> <model fallback="forbid">kvm64</model>
>> </cpu>
>> <clock offset="utc"/>
>> <on_poweroff>destroy</on_poweroff>
>> <on_reboot>restart</on_reboot>
>> <on_crash>restart</on_crash>
>> <devices>
>> <emulator>/usr/bin/qemu-system-x86_64</emulator>
>> <disk type="file" device="cdrom">
>> <driver name="qemu" type="raw"/>
>> <target dev="hdc" bus="ide"/>
>> <readonly/>
>> <address type="drive" controller="0" bus="1" target="0"
>> unit="0"/>
>> </disk>
>> <disk type="file" device="disk">
>> <driver name="qemu" type="qcow2" cache="writethrough"/>
>> <source file="/mnt/nvme1/VIRTUAL_MACHINES/slacky-0.qcow2"/>
>> <target dev="vda" bus="virtio"/>
>> <boot order="1"/>
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x09"
>> function="0x0"/>
>> </disk>
>> <controller type="usb" index="0" model="ich9-ehci1">
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x05"
>> function="0x7"/>
>> </controller>
>> <controller type="usb" index="0" model="ich9-uhci1">
>> <master startport="0"/>
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x05"
>> function="0x0" multifunction="on"/>
>> </controller>
>> <controller type="usb" index="0" model="ich9-uhci2">
>> <master startport="2"/>
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x05"
>> function="0x1"/>
>> </controller>
>> <controller type="usb" index="0" model="ich9-uhci3">
>> <master startport="4"/>
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x05"
>> function="0x2"/>
>> </controller>
>> <controller type="ide" index="0">
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x01"
>> function="0x1"/>
>> </controller>
>> <controller type="virtio-serial" index="0">
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x07"
>> function="0x0"/>
>> </controller>
>> <controller type="scsi" index="0" model="virtio-scsi">
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x08"
>> function="0x0"/>
>> </controller>
>> <controller type="pci" index="0" model="pci-root"/>
>> <interface type="network">
>> <mac address="52:54:00:c3:93:40"/>
>> <source network="default"/>
>> <model type="virtio"/>
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x03"
>> function="0x0"/>
>> </interface>
>> <serial type="file">
>> <source path="/tmp/myconsoleoutput.txt"/>
>> <target type="isa-serial" port="0">
>> <model name="isa-serial"/>
>> </target>
>> </serial>
>> <console type="file">
>> <source path="/tmp/myconsoleoutput.txt"/>
>> <target type="serial" port="0"/>
>> </console>
>> <input type="tablet" bus="usb">
>> <address type="usb" bus="0" port="1"/>
>> </input>
>> <input type="mouse" bus="ps2"/>
>> <input type="keyboard" bus="ps2"/>
>> <graphics type="spice" autoport="yes" listen="127.0.0.1">
>> <listen type="address" address="127.0.0.1"/>
>> </graphics>
>> <sound model="ich9">
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x04"
>> function="0x0"/>
>> </sound>
>> <audio id="1" type="spice"/>
>> <video>
>> <model type="qxl" ram="65536" vram="65536" vgamem="16384"
>> heads="1" primary="yes"/>
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x02"
>> function="0x0"/>
>> </video>
>> <memballoon model="virtio">
>> <address type="pci" domain="0x0000" bus="0x00" slot="0x06"
>> function="0x0"/>
>> </memballoon>
>> </devices>
>> </domain>
>>
>>
>> And the guest log with the generated command line:
>>
>> 2022-02-20 01:13:12.985+0000: starting up libvirt version: 7.8.0,
>> qemu version: 6.1.0, kernel: 5.15.19, hostname: godzilla.peecee3.com
>> LC_ALL=C \
>> PATH=/sbin:/usr/sbin:/bin:/usr/bin \
>> HOME=/var/lib/libvirt/qemu/domain-34-slacky-0 \
>> XDG_DATA_HOME=/var/lib/libvirt/qemu/domain-34-slacky-0/.local/share \
>> XDG_CACHE_HOME=/var/lib/libvirt/qemu/domain-34-slacky-0/.cache \
>> XDG_CONFIG_HOME=/var/lib/libvirt/qemu/domain-34-slacky-0/.config \
>> /usr/bin/qemu-system-x86_64 \
>> -name guest=slacky-0,process=qemu:slacky-0,debug-threads=on \
>> -S \
>> -object
>> '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/var/lib/libvirt/qemu/domain-34-slacky-0/master-key.aes"}'
>> \
>> -machine
>> pc-i440fx-5.1,accel=kvm,usb=off,dump-guest-core=off,memory-backend=pc.ram \
> So this instructs qemu to use a memory device wih id='pc.ram' as the
> default/generic memory for the guest..
>
>> -cpu kvm64 \
>> -m 4096 \
>> -overcommit mem-lock=off \
> .. but we never generate such device. Here libvirt should have generated
> -object memory-backend-file,id=pc.ram,path=/hugepages/...
>
> And I think I know why. Let me post a patch.
>
>> -smp 2,sockets=2,cores=1,threads=1 \
>> -uuid 4a67eb39-9b92-8b8a-97ba-7e1250d56b07 \
>> -no-user-config \
>> -nodefaults \
>> -chardev socket,id=charmonitor,fd=34,server=on,wait=off \
>> -mon chardev=charmonitor,id=monitor,mode=control \
>> -rtc base=utc \
>> -no-shutdown \
>> -boot menu=off,strict=on \
>> -device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 \
>> -device
>> ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5
>> \
>> -device
>> ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x5.0x1 \
>> -device
>> ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2 \
>> -device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x8 \
>> -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x7 \
>> -device ide-cd,bus=ide.1,unit=0,id=ide0-1-0 \
>> -blockdev
>> '{"driver":"file","filename":"/mnt/nvme1/VIRTUAL_MACHINES/slacky-0.qcow2","node-name":"libvirt-1-storage","cache":{"direct":false,"no-flush":false},"auto-read-only":true,"discard":"unmap"}'
>> \
>> -blockdev
>> '{"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":false,"no-flush":false},"driver":"qcow2","file":"libvirt-1-storage","backing":null}'
>> \
>> -device
>> virtio-blk-pci,bus=pci.0,addr=0x9,drive=libvirt-1-format,id=virtio-disk0,bootindex=1,write-cache=off
>> \
>> -netdev tap,fd=58,id=hostnet0,vhost=on,vhostfd=60 \
>> -device
>> virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:c3:93:40,bus=pci.0,addr=0x3
>> \
>> -add-fd set=3,fd=62 \
>> -chardev file,id=charserial0,path=/dev/fdset/3,append=on \
>> -device isa-serial,chardev=charserial0,id=serial0 \
>> -device usb-tablet,id=input0,bus=usb.0,port=1 \
>> -audiodev id=audio1,driver=spice \
>> -spice
>> port=5901,addr=127.0.0.1,disable-ticketing=on,seamless-migration=on \
>> -device
>> qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2
>> \
>> -device ich9-intel-hda,id=sound0,bus=pci.0,addr=0x4 \
>> -device
>> hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0,audiodev=audio1 \
>> -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 \
>> -msg timestamp=on
>> 2022-02-20T01:13:13.136602Z qemu-system-x86_64: Memory backend
>> 'pc.ram' not found
>> 2022-02-20 01:13:13.186+0000: shutting down, reason=failed
>>
>> Again, thank you!
>>
>> Michal
Many thanks!
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