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

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Message-ID: <87frx5ozrg.fsf@all.your.base.are.belong.to.us>
Date: Tue, 05 Mar 2024 09:21:07 +0100
From: Björn Töpel <bjorn@...nel.org>
To: Conor Dooley <conor.dooley@...rochip.com>, Anup Patel
 <apatel@...tanamicro.com>
Cc: Conor Dooley <conor@...nel.org>, Alexandre Ghiti
 <alexghiti@...osinc.com>, Anup Patel <anup@...infault.org>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer
 Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Andrea
 Parri <andrea@...osinc.com>, Samuel Holland <samuel.holland@...ive.com>,
 Steven
 Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, Mark
 Rutland <mark.rutland@....com>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 Björn Töpel <bjorn@...osinc.com>, Andrea Parri
 <parri.andrea@...il.com>
Subject: Re: [PATCH v3 2/2] riscv: Fix text patching when IPI are used

Conor Dooley <conor.dooley@...rochip.com> writes:

> On Tue, Mar 05, 2024 at 08:33:30AM +0530, Anup Patel wrote:
>> On Tue, Mar 5, 2024 at 1:54 AM Björn Töpel <bjorn@...nel.org> wrote:
>> >
>> > Conor Dooley <conor@...nel.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@...osinc.com>
>> > >> Signed-off-by: Björn Töpel <bjorn@...osinc.com>
>> > >> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
>> > >> Reviewed-by: Andrea Parri <parri.andrea@...il.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.
>
> Whether or not this is backportable, if it fixes a bug, it should get
> a Fixes: tag for the commit that it fixes. Fixes: isn't "the backport"
> tag, cc: stable is.

I guess the question is if this *is* a fix, or rather a change required
for AIA (not a fix).