RFR: 8348384: RISC-V: Disable auto-enable Vector on buggy kernels [v2]

[Fei Yang]

On Mon, 27 Jan 2025 07:41:33 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Hi please consider!
>> 
>> Linux kernels pre-6.9 can copy a dirty v-state during signal return path:
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/riscv/kernel/signal.c?h=v6.13-rc1&id=c27fa53b858b4ee6552a719aa599c250cf98a586
>> 
>> We should not auto-enable vector with such kernel, as we must be able to receive signals during the execution of vector code.
>> 
>> Manual tested pre and post 6.9 as expected.
>> 
>> Thanks, Robbin
>
> Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Update for merge
>  - Merge branch 'master' into no_V_69
>  - No V <6.9

src/hotspot/os_cpu/linux_riscv/riscv_hwprobe.cpp line 174:

> 172:       LogMessage(os) log;
> 173:       if (log.is_info()) {
> 174:         log.info("Linux kernels before 6.9 (current %ld.%ld) have a known bug when using Vector and signals.", major, minor);

You might want to update the 6.9 version number in this log info as well. Looks good otherwise.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23256#discussion_r1930089241