RFR: 8297697: RISC-V: Add support for SATP mode detection

[Ludovic Henry]

On Mon, 28 Nov 2022 11:31:17 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

> RISC-V gets sv57-based virtual memory support since Linux 5.18 [1]. There are some reports of the OpenJDK RISC-V port crashing on Linux 5.18+ with QEMU-system 7.10+ when sv57 was enabled [2][3] as currently RISC-V port only supports up to sv48.
> As discussed in [3], given the fact that there are no existing boards or hardware even support anything more than sv48,
> we decide to add detection for SATP (Supervisor Address Translation and Protection) mode at JVM startup time if possible and explicitly issue a warning and stop early when sv57 is enabled.
> 
> When sv57 is enabled, the output of java -version would be:
> 
> 
> root at qemuriscv64:~# jdk/bin/java -version
> Error occurred during initialization of VM
> Unsupported satp mode: 10
> 
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=aa5b537b0ecc16992577b013f11112d54c7ce869
> [2] https://mail.openjdk.org/pipermail/riscv-port-dev/2022-September/000639.html
> [3] https://mail.openjdk.org/pipermail/riscv-port-dev/2022-November/000681.html
> 
> Testing:
> 
> - QEMU-system with sv48/sv57-enabled Linux image `-version` test
> - HiFive Unmatched board (sv39) `-version` test

src/hotspot/cpu/riscv/vm_version_riscv.cpp line 43:

> 41:   VM_MODE mode = get_satp_mode();
> 42:   if (mode > RISCV64_ONLY(VM_SV48) RISCV32_ONLY(VM_SV32)) {
> 43:     vm_exit_during_initialization(err_msg("Unsupported satp mode: %d", mode));

I would map that number to a string. For example 10 to “sv48” so it is more googlable and searchable.

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PR: https://git.openjdk.org/jdk/pull/11388