Hello Steve,
Thank you for posting the qemu cpr-transfer patches on qemu-devel. I am
experimenting with them, and I noticed that cpr-transfer is failing on some
qemu machine types. cpr-transfer is working for me on the microvm machine type
but failing on q35 and pc-i440fx. When running in those configurations I get
the following error on the new qemu process:
qemu-system-x86_64: error while loading state for instance 0x0 of device
'kvm-tpr-opt'
2025-02-18T14:46:52.550319Z qemu-system-x86_64: load of migration failed:
Operation not permitted
The issue occurs when initializing the vapic device in the new qemu process. In
vapic_map_rom_writable, rom_size is set to zero. This causes the following
condition to be triggered:
ram = memory_region_get_ram_ptr(section.mr);
rom_size = ram[rom_paddr + 2] * ROM_BLOCK_SIZE;
if (rom_size == 0) {
return -1;
}
This occurs on the qemu master branch (tested on commit
9736ee382e95ead06a838fe0b0498e0cb3845270) with the following qemu command line
options:
Terminal 1:
/opt/qemu-build/bin/qemu-system-x86_64 -nographic -cpu
host,migratable=yes,-vmx,-svm,invpcid=off -display
vnc=unix:/opt/bchaney-tmp/vnc.socket -enable-kvm -name
bchaney_test1,debug-threads=on -smp 4 -object
memory-backend-file,id=ram0,size=4G,mem-path=/dev/shm/ram0,share=on -m 4G
-machine aux-ram-share=on -rtc clock=vm -no-user-config -nodefaults -msg
timestamp=on -bios /opt/linode-seabios/roms/bios.bin -machine q35,accel=kvm
-cdrom /opt/bchaney-tmp/ubuntu-24.04.1-live-server-amd64.iso -qmp stdio
Terminal 2:
/opt/qemu-build/bin/qemu-system-x86_64 -nographic -cpu
host,migratable=yes,-vmx,-svm,invpcid=off -display
vnc=unix:/opt/bchaney-tmp/vnc.socket -enable-kvm -name
bchaney_test1,debug-threads=on -smp 4 -object
memory-backend-file,id=ram0,size=4G,mem-path=/dev/shm/ram0,share=on -m 4G
-machine aux-ram-share=on -rtc clock=vm -no-user-config -nodefaults -msg
timestamp=on -bios /opt/linode-seabios/roms/bios.bin -machine q35,accel=kvm
-cdrom /opt/bchaney-tmp/ubuntu-24.04.1-live-server-amd64.iso -incoming
'{"channel-type": "main", "addr": { "transport": "socket", "type": "unix",
"path": "/opt/bchaney-tmp/main.sock"}}' -incoming '{"channel-type": "cpr",
"addr": { "transport": "socket", "type": "unix", "path":
"/opt/bchaney-tmp/cpr.sock"}}' -monitor stdio
Qmp commands executed (in Terminal 1):
{"execute":"qmp_capabilities"}
{"execute": "query-status"}
{"execute":"migrate-set-parameters",
"arguments":{"mode":"cpr-transfer"}}
{"execute": "migrate", "arguments": { "channels": [
{"channel-type": "main", "addr": { "transport": "socket", "type":
"unix",
"path": "/opt/bchaney-tmp/main.sock"}},
{"channel-type": "cpr",
"addr": { "transport": "socket", "type": "unix",
"path": "/opt/bchaney-tmp/cpr.sock"}}]}}
{"execute": "query-status"}
Is this a hardware configuration that is currently intended to be supported? If
not, will it be supported in the future?
Thank you,
Ben Chaney
