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Date: Thu, 23 May 2024 15:13:50 +0100
From: Conor Dooley <conor@kernel.org>
To: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: 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>,
	Andrea Parri <parri.andrea@gmail.com>,
	=?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <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
Message-ID: <20240523-showcase-helpful-4cc84fe2f1d5@spud>
References: <20240523115134.70380-1-alexghiti@rivosinc.com>
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On Thu, May 23, 2024 at 01:51:34PM +0200, Alexandre Ghiti wrote:
> 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.
>=20
> 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).
>=20
> This caused crashes on multiple HW as reported by Conor and Bj=F6rn 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.
>=20
> Fixes: c97bf629963e ("riscv: Fix text patching when IPI are used")
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Reported-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>

Thanks for the quick fix Alex :)

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