Agilex™ 5 ES Device Errata and User Guidelines

ID 825514
Date 12/09/2024
Public
Document Table of Contents

3.1.3. 2441007: Completion of affected memory accesses might not be guaranteed by completion of a TLBI

Description

The core might not guarantee completion of all memory accesses after completion of a TLB Invalidate (TLBI) instruction affecting those accesses on another core.

Conditions

  1. Another PE in the system executes a TLBI or Instruction Cache (IC) instruction, followed by a Data Synchronization Barrier (DSB) instruction.
  2. The core executes a store to a memory location A.
  3. Another PE in the system modifies the descriptor used by the store to memory location A, using a break-before-make sequence. The break-before-make sequence will include a TLBI instruction, followed by a DSB instruction.
  4. Rare, timing-sensitive, microarchitectural conditions occur.

Impact

The DSB used after the TLBI as part of the break-before-make sequence might not guarantee the completion of the store to memory location A under very rare and unlikely timing conditions. For most systems and applications, the latency of the break-before-make sequence and time until later reuse is very likely to exceed the latency required to naturally complete the store.

Workaround

Given the rarity of the conditions needed to trigger this erratum, a workaround is not expected to be needed in most systems.

If a workaround is required, then the TLBI, DSB sequence from the break-before-make sequence can be repeated. After repeating the TLBI, DSB sequence, all memory accesses that use a translation changed by the break-before-make sequence will have completed.

Category

Category B (rare)