RFR: 8378107: Data cache zeroing is used even when it is prohibited

[Aleksey Shipilev]

On Tue, 17 Feb 2026 16:24:48 GMT, Andrew Haley <aph at openjdk.org> wrote:

> The DC ZVA instruction should not be used when DZP, bit [4] in DCZID_EL0, is set.
> 
> It turns out that detection of DZP, bit [4] in DCZID_EL0, never worked. And this was never a problem until now, because everyone supports DC ZVA instructions.

So, to confirm, this is how `_zva_length` is initialized:


  if (!(dczid_el0 & 0x10)) {
    _zva_length = 4 << (dczid_el0 & 0xf);
  }


When we do not take this branch, `_zva_length` remains at `0`, and so `is_zva_enabled()` should return `false`.

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29762#pullrequestreview-3815187601