Fixup tlbie vs store ordering issue on POWER9

Bug #1848193 reported by bugproxy on 2019-10-15
This bug affects 1 person
Affects Status Importance Assigned to Milestone
The Ubuntu-power-systems project
Canonical Kernel Team
linux (Ubuntu)
Manoj Iyer

Bug Description

== Comment: #0 - Michael Ranweiler - 2019-10-07 01:52:38 ==
On POWER9, under some circumstances, a broadcast TLB invalidation will fail to invalidate the ERAT cache on some threads when there are parallel mtpidr/mtlpidr happening on other threads of the same core. This can cause stores to continue to go to a page after it's unmapped.

The workaround is to force an ERAT flush using PID=0 or LPID=0 tlbie flush. This additional TLB flush will cause the ERAT cache invalidation. Since we are using PID=0 or LPID=0, we don't get filtered out by the TLB snoop filtering logic.

We need to still follow this up with another tlbie to take care of store vs tlbie ordering issue explained in commit: a5d4b5891c2f ("powerpc/mm: Fixup tlbie vs store ordering issue on POWER9"). The presence of ERAT cache implies we can still get new stores and they may miss store queue marking flush.

The upstream git commits to resolve the problem:

bugproxy (bugproxy) on 2019-10-15
tags: added: architecture-ppc64le bugnameltc-181791 severity-medium targetmilestone-inin---
Changed in ubuntu:
assignee: nobody → Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
affects: ubuntu → linux (Ubuntu)
Changed in ubuntu-power-systems:
assignee: nobody → Canonical Kernel Team (canonical-kernel-team)
importance: Undecided → Medium
Manoj Iyer (manjo) on 2019-10-18
Changed in linux (Ubuntu):
assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) → Manoj Iyer (manjo)
importance: Undecided → Medium
Manoj Iyer (manjo) wrote :

IBM can you please test the Eoan kernel in this PPA:

Also, please share the following information with us:

1. Your testcase, and instructions on how to run the test cases.
2. Your system config information and firmware levels.
3. Is there any significant customer impact if this is not backported to earlier releases?

Manoj Iyer (manjo) on 2019-10-21
Changed in linux (Ubuntu):
status: New → In Progress
Changed in ubuntu-power-systems:
status: New → In Progress
Manoj Iyer (manjo) on 2019-10-22
Changed in linux (Ubuntu):
status: In Progress → Incomplete
Changed in ubuntu-power-systems:
status: In Progress → Incomplete
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