Series Z and POWER up to and including POWER9 are susceptible to meltdown as well.

https://www.zdnet.com/article/meltdown-spectre-ibm-preps-fir...

Ok. debian is even more explicit than suse above regarding "no meltdown on Z":

https://wiki.debian.org/DebianSecurity/SpectreMeltdown#Syste...

But, not 7400 G4 and earlier.

https://tenfourfox.blogspot.com/2018/01/actual-field-testing...

Which aren't POWER cores. POWER is an IBM trademark; the 7400 is a Motorola PowerPC core.

A fair point, though early POWER cores probably aren't for the same reasons these aren't (can't speculate through indirect branches using SPRs), and IBM was involved in the development of both.