RFR: 8370947: Mitigate Neoverse-N1 erratum 1542419 negative impact on GenZGC performance [v3]

[Andrew Haley]

On Mon, 24 Nov 2025 20:56:32 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

> It's a bit surprising to me if they invalidate all TLB entries, effectively ripping out the entire virtual address space, even when a range is passed in. If so,

"Because the cache-maintenance wasn't needed, we can do the TLBI instead.
In fact, the I-Cache line-size isn't relevant anymore, we can reduce
the number of traps by producing a fake value.

"For user-space, the kernel's work is now to trap CTR_EL0 to hide DIC,
and produce a fake IminLine. EL3 traps the now-necessary I-Cache
maintenance and performs the inner-shareable-TLBI that makes everything
better."

My interpretation of this is that we only need to do the synchronization dance once, at the end of the patching. But I guess we don't know exactly if we have an affected core or if the kernel workaround is in action.

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PR Comment: https://git.openjdk.org/jdk/pull/28328#issuecomment-3575547686