On 2/19/2025 4:12 PM, Fabiano Rosas wrote:
"Chaney, Ben" <bcha...@akamai.com> writes: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; }Good job debugging the most opaque error message the migration code can emit.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 stdioYou're missing an option that tells QEMU to actually make use of the shared memory backend: -machine memory-backend=ram0 You might be looking at an older version of the documentation. We've fixed that and Steve is working on a better error message for it.
Thank-you Fabiano for replying. I was OOTO last week. Ben, let me know if -machine memory-backend=ram0 does not fix the problem. - Steve
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
