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From: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
To: Alexandre Ghiti <alexghiti@rivosinc.com>, Paul Walmsley
 <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou
 <aou@eecs.berkeley.edu>, Steven Rostedt <rostedt@goodmis.org>, Masami
 Hiramatsu <mhiramat@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
 Alexandre Ghiti <alexghiti@rivosinc.com>, Andrea Parri
 <parri.andrea@gmail.com>, =?utf-8?B?QmrDtnJuIFTDtnBlbA==?=
 <bjorn@rivosinc.com>, Conor Dooley
 <conor.dooley@microchip.com>, linux-riscv@lists.infradead.org,
 linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Fix early ftrace nop patching
In-Reply-To: <20240523115134.70380-1-alexghiti@rivosinc.com>
References: <20240523115134.70380-1-alexghiti@rivosinc.com>
Date: Thu, 23 May 2024 14:48:55 +0200
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Alexandre Ghiti <alexghiti@rivosinc.com> 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 Bj=C3=B6rn si=
nce
> 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@rivosinc.com>

Nice!

I've manged to reproduce the crash on the VisionFive2 board (however
only triggered when CONFIG_RELOCATABLE=3Dy), and can verify that this fix
solves the issue.

Reviewed-by: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>
Tested-by: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>