Re: [PATCH] riscv: Fix early ftrace nop patching

[Björn Töpel]

Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> writes:

> Commit c97bf629963e ("riscv: Fix text patching when IPI are used")
> converted ftrace_make_nop() to use patch_insn_write() which does not
> emit any icache flush relying entirely on __ftrace_modify_code() to do
> that.
>
> But we missed that ftrace_make_nop() was called very early directly when
> converting mcount calls into nops (actually on riscv it converts 2B nops
> emitted by the compiler into 4B nops).
>
> This caused crashes on multiple HW as reported by Conor and Björn since
> the booting core could have half-patched instructions in its icache
> which would trigger an illegal instruction trap: fix this by emitting a
> local flush icache when early patching nops.
>
> Fixes: c97bf629963e ("riscv: Fix text patching when IPI are used")
> Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>

Nice!

I've manged to reproduce the crash on the VisionFive2 board (however
only triggered when CONFIG_RELOCATABLE=y), and can verify that this fix
solves the issue.

Reviewed-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
Tested-by: Björn Töpel <bjorn@xxxxxxxxxxxx>