Comment 45 for bug 1873809

Alright, at least partially understanding things now. So it looks like "Decoding failed" happens generally on some platforms (and I do not understand still why this is). The difference between the generic kernel and the kvm kernel is that the kvm kernel has a built-in BLK_DEV_RAM of size (4096) whereas the generic kernel uses a module for that.

It looks like only if BLK_DEV_RAM=y is set, the code which populates the initial rootfs does try to flush and refill the ramdisk device. Otherwise the partially expanded rootfs is retained. And I guess the ramdisk size is set to small so we get the incomplete write there.

I guess the solution (which does not solve the decode failure) is to change the kvm kernel config to

BLK_DEV_RAM=m
CONFIG_BLK_DEV_RAM_SIZE=65536