From: Steven Rostedt <rostedt@goodmis.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
Julien Thierry <julien.thierry@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
AKASHI Takahiro <takahiro.akashi@linaro.org>,
Ingo Molnar <mingo@redhat.com>, Torsten Duwe <duwe@lst.de>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Amit Daniel Kachhap <amit.kachhap@arm.com>,
live-patching@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6] arm64: implement ftrace with regs
Date: Fri, 4 Jan 2019 13:06:48 -0500 [thread overview]
Message-ID: <20190104130648.02657f3f@gandalf.local.home> (raw)
In-Reply-To: <20190104175017.GA7157@lakrids.cambridge.arm.com>
On Fri, 4 Jan 2019 17:50:18 +0000
Mark Rutland <mark.rutland@arm.com> wrote:
> At Linux Plumbers, I had a conversation with Steve Rostedt, and we came
> to the conclusion that (withut heavyweight synchronization) patching two
> NOPs at runtime isn't safe, since a CPU might have executed the first
> NOP as a NOP before another CPU patches both instructions. So a CPU
> might execute:
>
> NOP
> BL ftrace_regs_caller
>
> ... rather than the expected:
>
> MOV X9, X30
> BL ftrace_regs_caller
>
> ... and therefore X9 contains some UNKNOWN value, rather than the
> original LR value.
>
> I wonder if we could solve that by patching the kernel at build-time, to
> add the MOV X9, X30 in place of the first NOP. If we were to do that, we
> could also update the addresses to pooint at the second NOP, simplifying
> the changes to the runtime code.
You can also patch it at boot up when there's only one CPU running, and
interrupts are disabled.
-- Steve
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next prev parent reply other threads:[~2019-01-04 18:06 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-04 14:10 [PATCH v6] arm64: implement ftrace with regs Torsten Duwe
2019-01-04 17:50 ` Mark Rutland
2019-01-04 18:06 ` Steven Rostedt [this message]
2019-01-04 22:41 ` Torsten Duwe
2019-01-05 11:05 ` Torsten Duwe
2019-01-05 20:00 ` Steven Rostedt
2019-01-07 11:19 ` Mark Rutland
2019-01-14 12:13 ` Balbir Singh
2019-01-14 12:26 ` Mark Rutland
2019-01-16 15:56 ` Julien Thierry
2019-01-16 18:01 ` Julien Thierry
2019-01-07 4:57 ` Amit Daniel Kachhap
2019-01-16 9:57 ` Julien Thierry
2019-01-16 10:08 ` Julien Thierry
2019-01-17 15:48 ` Torsten Duwe
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