Eben Upton (Raspberry Pi founder) posted a good explanation of the processor flaws and why the Raspberry Pi is immune (basically because it uses an older version of the ARM core that doesn't do any/as much speculative execution as more modern Intel/AMD/ARM chips).
Why Raspberry Pi isn't vulnerable to Spectre or Meltdown - Raspberry Pi
Although all the newer chips from all the manufacturers are vunerable to some extent, it's still Intel chips that have the greatest vulnerabilities and will slow down the most when patches are applied to work around the flaws. The only real answer to the security problem without slowing things down is a complete redesign of the way speculative execution (hence 'Spectre') is carried out by all modern multi-core chips. This will likely take years.