linux-kernel - Re: [PATCH] riscv: Fix early ftrace nop patching

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Date: Thu, 23 May 2024 15:13:50 +0100
From: Conor Dooley <conor@...nel.org>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Andrea Parri <parri.andrea@...il.com>,
	Björn Töpel <bjorn@...osinc.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Fix early ftrace nop patching

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.
> 
> 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@...osinc.com>

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

Thanks for the quick fix Alex :)

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