ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Common Memory System Architecture Features
B2.2.5 The interaction of cache lockdown with cache maintenance
The interaction of cache lockdown and cache maintenance operations is IMPLEMENTATION DEFINED.
However, an architecturally-defined cache maintenance operation on a locked cache line must comply with
the following general rules:
The effect of these operations on locked cache entries is IMPLEMENTATION DEFINED:
— cache clean by set/way
— cache invalidate by set/way
— cache clean and invalidate by set/way
— instruction cache invalidate all.
However, one of the following approaches must be adopted in all these cases:
1. If the operation specified an invalidation a locked entry is not invalidated from the cache. If the
operation specified a clean it is IMPLEMENTATION DEFINED whether locked entries are cleaned.
2. If an entry is locked down, or could be locked down, an IMPLEMENTATION DEFINED Data Abort
exception is generated, using the fault status code defined for this purpose in CP15 c5, see
either:
Fault Status and Fault Address registers in a VMSA implementation on page B3-48
Fault Status and Fault Address registers in a PMSA implementation on page B4-18.
This permits a typical usage model for cache invalidate routines to operate on a large range of
addresses by performing the required operation on the entire cache, without having to consider
whether any cache entries are locked. The operation performed is either an invalidate, or a clean and
invalidate.
The effect of these operations is IMPLEMENTATION DEFINED:
— cache clean by MVA
— cache invalidate by MVA
— cache clean and invalidate by MVA.
However, one of the following approaches must be adopted in all these cases:
1. If the operation specified an invalidation a locked entry is invalidated from the cache. For the
clean and invalidate operation, the entry must be cleaned before it is invalidated.
2. If the operation specified an invalidation a locked entry is not invalidated from the cache. If the
operation specified a clean it is IMPLEMENTATION DEFINED whether locked entries are cleaned
3. If an entry is locked down, or could be locked down, an IMPLEMENTATION DEFINED Data Abort
exception is generated, using the fault status code defined for this purpose in CP15 c5, see
either:
Fault Status and Fault Address registers in a VMSA implementation on page B3-48
Fault Status and Fault Address registers in a PMSA implementation on page B4-18.
An implementation that uses the abort mechanisms for entries that could be locked must:
document IMPLEMENTATION DEFINED code sequences that then perform the required operation on
entries that are not locked down
B2-18 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B