Meltdown fix for Power
PowerPC Memory Protection Keys In For Linux 4.16, Power Has Meltdown Mitigation In 4.15 (Phoronix)
powerpc/64s: Add support for RFI flush of L1-D cache (git commit)
According to the git commit, this fixes Meltdown on POWER7, POWER8 and POWER9. He explicitly states they don’t know if the 970 (Apple G5), pasemi CPUs (AmigaOne X1000) or Freescale CPUs are vulnerable.
According to the commit, Meltdown on the affected chips only works on the L1 cache, so the fix purges L1 when switching to a less privileged state (kernel to userspace).
In order for [the vulnerability] to happen, the first load must hit in the L1, because before the load is sent to the L2 the permission check is performed. Therefore if no kernel addresses hit in the L1 the vulnerability can not occur. We can ensure that is the case by flushing the L1 whenever we return to userspace. Similarly for hypervisor vs guest.
Also it sounds like these patches should help even without a firmware fix:
Newer firmwares are able to advertise to us that there is a special nop instruction that flushes the L1-D. If we do not see that advertised, we fall back to doing a displacement flush in software.
Edit: looks like @catsay beat me to it: