Snapshots freeze guest Sabrelite IMX.6 board
Hello, I'm trying to take and restore a snapshot with the whole system state of the Sabrelite IMX.6 board running on QEMU with commands savevm/loadvm. It seems that I am able to take a snapshot but loading the snapshot fails. For comparison I checked out snapshots on 32bit ARM Virt with Debian as well as on the Versatilepb board with a bare metal application and it works fine. The problem occurs only with that one particular board. My environment is: Ubuntu 18.04 QEMU 3.0.1 (I see the same issue in QEMU 4.0.0 as well) The kernel and device tree used for the board was 5.1.14 version from kernel.org The file system was build from imx_v6_v7_defconfig config in buildroot as and sd card image. Problem: Loading snapshot stops the whole machine and it's impossible to resume it. Steps to reproduce problem: 1. I converted the sdcard.img built from the buildroot to qcow2 using command qemu-img convert -f raw -O qcow2 sdcard.img sdcard.qcow2, since the raw doesn't support snapshots. 2. I start QEMU with a command ./arm-softmmu/qemu-system-arm -m 512 -M sabrelite -kernel zImage -append "rootfstype=ext4 root=/dev/mmcblk2p2 rw rootwait" -rtc base=localtime,clock=vm -dtb imx6dl-sabresd.dtb -drive file=sdcard.qcow2,index=2,format=qcow2,id=mycard -device sd- card,drive=mycard -nographic -net nic -net user 3. I run a simple program which print characters to the console in the background and add some files in user directory, to differ from original image. 4. I switch to QEMU monitor, and type “savevm <name>”. When I type “info snapshots”, the snapshot is listed. So I assume it was saved correctly. 5. Then I switch back to Linux console from monitor, remove the added files and stop the background printing process. 6. I switch back to monitor and I'm trying now to load the snapshot by “loadvm <name>” command. That’s where the problem occurs. QEMU stops and I can't switch back from monitor to Linux. Typing “cont” doesn’t help. It seems like the simulation has freezed. CPU usage on my Laptop machine equals 100% until I exit QEMU. What’s interesting when I exit the QEMU and then start it again the Linux boots and after it reaches the command prompt I can see the files which were removed after saving the snapshot. It looks like loading the snapshots works for restoring disk space but it fails for restoring the running processes. Due to the answer on QEMU mailing list (https://lists.nongnu.org/archive/html/qemu-discuss/2019-08/msg00016.html) it is QEMUs bug.
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