A5.4 Translation table walks

When the Cortex®-A55 core generates a memory access, the MMU:

  1. Performs a lookup for the requested VA and current translation regime in the relevant instruction or data L1 TLB.
  2. If there is a miss in the relevant L1 TLB, the MMU performs a lookup for the requested VA, current ASID, current VMID, and translation regime in the L2 TLB.
  3. If there is a miss in the L2 TLB, the MMU performs a hardware translation table walk.

In the case of an L2 TLB miss, the hardware does a translation table walk as long as the MMU is enabled, and the translation using the base register has not been disabled.

If the translation table walk is disabled for a particular base register, the core returns a Translation Fault. If the TLB finds a matching entry, it uses the information in the entry as follows.

The access permission bits and the domain determine if the access is permitted. If the matching entry does not pass the permission checks, the MMU signals a Permission fault. See the Arm® Architecture Reference Manual Armv8, for Armv8-A architecture profile for details of Permission faults, including:

  • A description of the various faults.
  • The fault codes.
  • Information regarding the registers where the fault codes are set.

    Note:

    In AArch32 VMSA Short-descriptor format, the permission check includes the domain properties.
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