8334890: Missing unconditional cross modifying fence in nmethod entry barriers

[bulasevich]

The change adds an unconditional memory barrier to guarantee the instruction fetcher observes the correct updated immediate.

Merge conflict caused by minor context difference (added comment in a mainline): fixed manually.

Testing: jtreg tier 1-3 on arm64 and x64.

Update. The backport is controversial: while the functional change is correct and necessary, it introduces a regression in SPECjvm2008: JDK-8337778

Update.

• https://bugs.openjdk.org/browse/JDK-8337778 is closed with Won't Fix resultion

SPECjvm2008-Derby-ZGC performance on linux-aarch64 is not affected with patch applied to jdk21u

• before:
  • Score on derby: 5375.49 ops/m
  • Score on derby: 5430.11 ops/m
  • Score on derby: 5413.50 ops/m
  • Score on derby: 5363.00 ops/m
  • Score on derby: 5359.83 ops/m
  • Score on derby: 5325.92 ops/m
  • Score on derby: 5464.94 ops/m
  • Score on derby: 5413.74 ops/m
• after:
  • Score on derby: 5476.12 ops/m
  • Score on derby: 5280.42 ops/m
  • Score on derby: 5446.40 ops/m
  • Score on derby: 5402.60 ops/m
  • Score on derby: 5470.78 ops/m
  • Score on derby: 5409.36 ops/m
  • Score on derby: 5403.56 ops/m
  • Score on derby: 5457.11 ops/m

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8334890 needs maintainer approval

Issue

• JDK-8334890: Missing unconditional cross modifying fence in nmethod entry barriers (Bug - P3)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/1131/head:pull/1131
$ git checkout pull/1131

Update a local copy of the PR:
$ git checkout pull/1131
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/1131/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 1131

View PR using the GUI difftool:
$ git pr show -t 1131

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/1131.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back bulasevich! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[mlbridge]

Webrevs

• 00: Full (ee14f19e)

[jerboaa]

It's not clear this change introduces a regression: https://bugs.openjdk.org/browse/JDK-8337778

Please clarify.