RFR: 8367137: RISC-V: Detect Zicboz block size via hwprobe [v3]

[Fei Yang]

On Tue, 9 Sep 2025 14:58:25 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> I checked with kernel/cpu guy, apperently "cache blocks size" is instruction dependent in cmo spec. It have nothing todo with cache line size. (in theory, but in practice to implement these in a high performance way they do) So you could have zic64b, with cboz size of 32 and zicbom size of 128.

Ah, that could mean a bug in `MacroAssembler::zero_dcache_blocks` which assumes that CBO.ZERO would zero a cache line instead of a cache block. We should use Zicboz block size detected here instead if it's not zero. (Also note that UseZicboz is experimental for now and it is only enabled in VM_Version::rivos_features())

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PR Comment: https://git.openjdk.org/jdk/pull/27155#issuecomment-3272833150