Fixup tlbie vs store ordering issue on POWER9

[bugproxy]

== 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:

https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?h=fixes&id=677733e296b5c7a37c47da391fc70a43dc40bd67

https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?h=fixes&id=09ce98cacd51fcd0fa0af2f79d1e1d3192f4cbb0

https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?h=fixes&id=047e6575aec71d75b765c22111820c4776cd1c43

[Manoj Iyer (manjo)]

IBM can you please test the Eoan kernel in this PPA: https://launchpad.net/~ubuntu-power-triage/+archive/ubuntu/lp1848193/

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)]

IBM, any progress on testing results ?

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2019-12-16 05:06 EDT-------
I tested the PPA kernel and it works. I did try a before kernel to verify.

You can test this out with the testcase from selftests - tools/testing/selftests/powerpc/mm/tlbie_test. I've used a witherspoon with OP920. The end result of this can be unexpected results.

[Andrew Cloke (andrew-cloke)]

Thanks for testing the PPA kernel. Moving back to "triaged".

[Manoj Iyer (manjo)]

Fixed by https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1848039

[Manoj Iyer (manjo)]

$ uname -a
Linux bobone 5.3.0-24-generic #26-Ubuntu SMP Thu Nov 14 01:12:58 UTC 2019 ppc64le ppc64le ppc64le GNU/Linux

$ sudo ./tlbie_test
start_cpu list:0
number of worker threads:4 + 1 snapshot thread
Allocated address:0x000075e535810000 + secondary map:0x000075e535570000
logdir at : /tmp/logdir-26561
Timeout: 1200 seconds
=================================
     Starting Test
     Mon Dec 16 16:59:06 2019
=================================

$

[Frank Heimes (fheimes)]

Cool, many thx Manoj!