So wait, sparc solaris is the only production unix with hardware memory tagging but also linux has it? Are we talking strict SUS compliant systems (current or former because for some reason solaris is no longer listed as such despite ostensibly still being compliant unless the SRUs have seriously FUBARed some things) or unices in general? because I'd argue anyone running SUS compliant systems out of anything other than their choice happening to be compliant is arguably even more niche than running AIX or Solaris for anything else