RFR: 8310656: RISC-V: __builtin___clear_cache can fail silently. [v3]

[Robbin Ehn]

> Hi, please consider.
> 
> We recently had a bug where user were missing permissions to use this syscall.
> Which caused crashing on, according to hs_err on things like "addi x11, x24, 0" with SIGILL.
> If it fails it is even possible to execute valid but 'old' instruction which may not lead to a crash, instead the program misbehaves.
> 
> To avoid this mess I suggest that we first test the syscall during vm init and we use it directly.
> This way we can make sure it never fails.
> 
> Tested failing syscall with qemu, tested t1 in qemu, t1 on jh7110 in-progress.

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 four additional commits since the last revision:

 - merge update and nits
 - Merge branch 'master' into 8310656
 - added back data barrier
   
   Signed-off-by: Robbin Ehn <rehn at rivosinc.com>
 - 8310656: RISC-V: __builtin___clear_cache can fail silently.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14670/files
  - new: https://git.openjdk.org/jdk/pull/14670/files/6b6e2dd9..46b59c60

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14670&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14670&range=01-02

  Stats: 5912 lines in 342 files changed: 3718 ins; 753 del; 1441 mod
  Patch: https://git.openjdk.org/jdk/pull/14670.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14670/head:pull/14670

PR: https://git.openjdk.org/jdk/pull/14670