8370947: Mitigate Neoverse-N1 erratum 1542419 negative impact on GenZGC performance

[eastig]

Arm Neoverse N1 erratum 1542419: "The core might fetch a stale instruction from memory which violates the ordering of instruction fetches". It is fixed in Neoverse N1 r4p1.

Neoverse-N1 implementations mitigate erratum 1542419 with a workaround:

• Disable coherent icache.
• Trap IC IVAU instructions.
• Execute:
  • tlbi vae3is, xzr
  • dsb sy

tlbi vae3is, xzr invalidates translations for all address spaces (global for address). It waits for all memory accesses using in-scope old translation information to complete before it is considered complete.

As this workaround has significant overhead, Arm Neoverse N1 (MP050) Software Developer Errata Notice version 29.0 suggests:

"Since one TLB inner-shareable invalidation is enough to avoid this erratum, the number of injected TLB invalidations should be minimized in the trap handler to mitigate the performance impact due to this workaround."

This PR introduces a mechanism to defer instruction cache (ICache) invalidation for AArch64 to address the Arm Neoverse N1 erratum 1542419, which causes significant performance overhead if ICache invalidation is performed too frequently. The implementation includes detection of affected Neoverse N1 CPUs and automatic enabling of the workaround for relevant Neoverse N1 revisions.

Changes include:

• Added a new diagnostic JVM flag NeoverseN1Errata1542419 to enable or disable the workaround for the erratum. The flag is automatically enabled for Neoverse N1 CPUs prior to r4p1, as detected during VM initialization.
• Introduced the ICacheInvalidationContext class to manage deferred ICache invalidation, with platform-specific logic for AArch64. This context is used to batch ICache invalidations, reducing performance impact. As the address for icache invalidation is not relevant, we use the nmethod's code start address.
• Provided a default (no-op) implementation for ICacheInvalidationContext on platforms where the workaround is not needed, ensuring portability and minimal impact on other architectures.
• Modified barrier patching and relocation logic (ZBarrierSetAssembler, ZNMethod, RelocIterator, and related code) to accept a defer_icache_invalidation parameter, allowing ICache invalidation to be deferred and later performed in bulk.

---

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

Issue

• JDK-8370947: Mitigate Neoverse-N1 erratum 1542419 negative impact on GenZGC performance (Enhancement - P2)

Contributors

• Axel Boldt-Christmas <[email protected]>

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/28328/head:pull/28328
$ git checkout pull/28328

Update a local copy of the PR:
$ git checkout pull/28328
$ git pull https://git.openjdk.org/jdk.git pull/28328/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 28328

View PR using the GUI difftool:
$ git pr show -t 28328

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/28328.diff

[eastig]

Based on master...xmas92:jdk:deferred_icache_invalidation

[bridgekeeper]

👋 Welcome back eastigeevich! 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.

[eastig]

/contributor add xmas92

[openjdk]

@eastig xmas92 was not found in the census.

Syntax: /contributor (add|remove) [@user | openjdk-user | Full Name <email@address>]. For example:

• /contributor add @openjdk-bot
• /contributor add duke
• /contributor add J. Duke <[email protected]>

User names can only be used for users in the census associated with this repository. For other contributors you need to supply the full name and email address.

[openjdk]

@eastig The following label will be automatically applied to this pull request:

• hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[eastig]

/contributor add aboldtch

[openjdk]

@eastig
Contributor Axel Boldt-Christmas <[email protected]> successfully added.

[eastig]

Hi @fisk @theRealAph @xmas92 @shipilev

I created this draft PR based on @xmas92 work master...xmas92:jdk:deferred_icache_invalidation

Alex wrote about his implementation in JDK-8370947:

The implementation I linked is very aarch64 centric. I would like to create a bit nicer abstraction for this to allow easier adaption for other platforms.

I see his changes touch other backends. I tried to minimize changes and to avoid them in other backends.
I don't think the concept of deferred icache invalidation will be used anywhere but for Neoverse-N1 errata.

This PR does not cover all cases in ZGC at the moment. It can be done as soon as we agree with a proper way to fix.

I'd like to hear your opinion which way we should choose:

• Abstraction of deferred icache invalidation supported in all backends.
• Concrete implementation focused on Neoverse-N1.