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

[Ludovic Henry]

On Thu, 23 Jan 2025 09:51:23 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

Marked as reviewed by luhenry (Committer).

src/hotspot/os_cpu/linux_riscv/riscv_hwprobe.cpp line 176:

> 174:         log.info("Linux kernels before 6.9 (current %ld.%ld) have a known bug when using Vector and signals.", major, minor);
> 175:         log.info("Vector not enabled automatically via hwprobe, but can be turned on with -XX:+UseRVV.");
> 176:       }

Couldn't you simply have:
Suggestion:

      log_info(
            "Linux kernels before 6.9 (current %ld.%ld) have a known bug when using Vector and signals.\n"
            "Vector not enabled automatically via hwprobe, but can be turned on with -XX:+UseRVV.",
            major, minor);

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PR Review: https://git.openjdk.org/jdk/pull/23256#pullrequestreview-2569767352
PR Review Comment: https://git.openjdk.org/jdk/pull/23256#discussion_r1926919273