linuxkit: Very slow boot on hardware without RDRAND support

Description

I’m seeing extremely slow boots on my PC-Engines APU2 system. It seems the slowdown is due to crng init sometimes taking ~2mins to initialize:

(ns: getty) linuxkit-000db94b0fb0:~# dmesg | grep random
[    0.000000] random: get_random_bytes called from start_kernel+0x92/0x4c8 with crng_init=0
[   26.615537] random: dhcpcd: uninitialized urandom read (112 bytes read)
[   50.070272] random: fast init done
[  150.070298] random: crng init done

It seems that the CPU (an AMD GX-412TC) does not support RDRAND, so I’m thinking this may be the cause:

linuxkit-000db94b0fb0:~# grep rdrand /proc/cpuinfo
linuxkit-000db94b0fb0:~# echo $?
1

Basically, I’m wondering if there’s a way for me to avoid this on this particular chip. I’m hoping to use this system as a home router, so ~2-3min (re)boot times aren’t ideal 😉.

Steps to reproduce the issue:

I iPXE-booted an APU2C4 system from an initrd/kernel generated based on getty.yml - the only modification is I changed cmdline to read console=ttyS0,115200.

Waiting for the shell to be fully available takes a long time - about 25s for the “fast init” and an additional 100s for the “crng init”.

Describe the results you received:

Very slow boot…

Describe the results you expected:

Faster boot times 😉

Additional information you deem important (e.g. issue happens only occasionally):

This may be related to #3032, though I’m not sure it’s the same issue.