Re: [PATCH v3 2/2] riscv: Fix text patching when IPI are used

From: Anup Patel <apatel@ventanamicro.com>
To: "Björn Töpel" <bjorn@kernel.org>
Cc: "Conor Dooley" <conor@kernel.org>,
	"Alexandre Ghiti" <alexghiti@rivosinc.com>,
	"Anup Patel" <anup@brainfault.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Andrea Parri" <andrea@rivosinc.com>,
	"Samuel Holland" <samuel.holland@sifive.com>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Masami Hiramatsu" <mhiramat@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org,
	"Björn Töpel" <bjorn@rivosinc.com>,
	"Andrea Parri" <parri.andrea@gmail.com>
Subject: Re: [PATCH v3 2/2] riscv: Fix text patching when IPI are used
Date: Tue, 5 Mar 2024 08:33:30 +0530	[thread overview]
Message-ID: <CAK9=C2Xjgr9_H-sHkmAAc95dAm2jd+_dxLUxSM3RM3NrQJFKGQ@mail.gmail.com> (raw)
In-Reply-To: <87msrdzqxi.fsf@all.your.base.are.belong.to.us>

On Tue, Mar 5, 2024 at 1:54 AM Björn Töpel <bjorn@kernel.org> wrote:
>
> Conor Dooley <conor@kernel.org> writes:
>
> > On Thu, Feb 29, 2024 at 01:10:56PM +0100, Alexandre Ghiti wrote:
> >> For now, we use stop_machine() to patch the text and when we use IPIs for
> >> remote icache flushes (which is emitted in patch_text_nosync()), the system
> >> hangs.
> >>
> >> So instead, make sure every CPU executes the stop_machine() patching
> >> function and emit a local icache flush there.
> >>
> >> Co-developed-by: Björn Töpel <bjorn@rivosinc.com>
> >> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
> >> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> >> Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
> >
> > What commit does this fix?
>
> Hmm. The bug is exposed when the AIA IPI are introduced, and used
> (instead of the firmware-based).
>
> I'm not sure this is something we'd like backported, but rather a
> prerequisite to AIA.
>
> @Anup @Alex WDYT?
>

The current text patching never considered IPIs being injected
directly in S-mode from hart to another so we are seeing this
issue now with AIA IPIs.

We certainly don't need to backport this fix since it's more
of a preparatory fix for AIA IPIs.

Regards,
Anup