ARMv8.1 is an extension to ARMv8, an ARM instruction set architecture which brought a large number of fundamental changes to the instruction set, including the introduction of 64-bit operating capabilities.

Mandatory Features from ARMv8.0

• CRC32 was optional in ARMv8.0, now mandatory.

Mandatory Features in ARMv8.1

• Large System Extensions (LSE)
  • New atomic instructions to support scalable performance:
  • Instructions for full-word, half-word, and byte operations are available.
  • Most of the following have optional load-acquire and/or store-release semantics.
    • Compare and Swap: CAS, CASP (up to 128-bit values).
    • Atomic Memory Operations: ADD, CLR, EOR, SET, MAX (signed/unsigned), MIN (signed/unsigned).
      • LD<op> versions return the value of the updated memory (LDADD for example).
      • ST<op> versions are "fire-and-forget" (STADD for example).
    • SWAP
• Rounding Double Multiply Add/Subtract instruction (RDMA)
• Limited Ordering Regions (LOR)
• Privileged access never (PAN)
• Virtualization Host Extensions (VHE)

Optional Features in ARMv8.1

• Hierarchical permission disables (HPD)
• 16-bute VMID (VMID16)
• PMU Extensions (PMU)