From: Dave Martin <Dave.Martin@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Jason Wang <jasowang@redhat.com>,
virtualization@lists.linux-foundation.org,
Arnd Bergmann <arnd@arndb.de>,
Alan Stern <stern@rowland.harvard.edu>,
Sami Tolvanen <samitolvanen@google.com>,
Matt Turner <mattst88@gmail.com>,
kernel-team@android.com, Marco Elver <elver@google.com>,
Kees Cook <keescook@chromium.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Josh Triplett <josh@joshtriplett.org>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
linux-arm-kernel@lists.infradead.org,
Richard Henderson <rth@twiddle.net>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org
Subject: Re: [PATCH 18/18] arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y
Date: Mon, 6 Jul 2020 17:08:20 +0100 [thread overview]
Message-ID: <20200706160820.GC10992@arm.com> (raw)
In-Reply-To: <20200630173734.14057-19-will@kernel.org>
On Tue, Jun 30, 2020 at 06:37:34PM +0100, Will Deacon wrote:
> When building with LTO, there is an increased risk of the compiler
> converting an address dependency headed by a READ_ONCE() invocation
> into a control dependency and consequently allowing for harmful
> reordering by the CPU.
>
> Ensure that such transformations are harmless by overriding the generic
> READ_ONCE() definition with one that provides acquire semantics when
> building with LTO.
>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
> arch/arm64/include/asm/rwonce.h | 63 +++++++++++++++++++++++++++++++
> arch/arm64/kernel/vdso/Makefile | 2 +-
> arch/arm64/kernel/vdso32/Makefile | 2 +-
> 3 files changed, 65 insertions(+), 2 deletions(-)
> create mode 100644 arch/arm64/include/asm/rwonce.h
>
> diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h
> new file mode 100644
> index 000000000000..515e360b01a1
> --- /dev/null
> +++ b/arch/arm64/include/asm/rwonce.h
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020 Google LLC.
> + */
> +#ifndef __ASM_RWONCE_H
> +#define __ASM_RWONCE_H
> +
> +#ifdef CONFIG_CLANG_LTO
> +
> +#include <linux/compiler_types.h>
> +#include <asm/alternative-macros.h>
> +
> +#ifndef BUILD_VDSO
> +
> +#ifdef CONFIG_AS_HAS_LDAPR
> +#define __LOAD_RCPC(sfx, regs...) \
> + ALTERNATIVE( \
> + "ldar" #sfx "\t" #regs, \
^ Should this be here? It seems that READ_ONCE() will actually read
twice... even if that doesn't actually conflict with the required
semantics of READ_ONCE(), it looks odd.
Making a direct link between LTO and the memory model also seems highly
spurious (as discussed in the other subthread) so can we have a comment
explaining the reasoning?
> + ".arch_extension rcpc\n" \
> + "ldapr" #sfx "\t" #regs, \
> + ARM64_HAS_LDAPR)
> +#else
> +#define __LOAD_RCPC(sfx, regs...) "ldar" #sfx "\t" #regs
> +#endif /* CONFIG_AS_HAS_LDAPR */
[...]
Cheers
---Dave
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next prev parent reply other threads:[~2020-07-06 16:09 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-30 17:37 [PATCH 00/18] Allow architectures to override __READ_ONCE() Will Deacon
2020-06-30 17:37 ` [PATCH 01/18] tools: bpf: Use local copy of headers including uapi/linux/filter.h Will Deacon
2020-07-01 16:38 ` Alexei Starovoitov
2020-06-30 17:37 ` [PATCH 02/18] compiler.h: Split {READ, WRITE}_ONCE definitions out into rwonce.h Will Deacon
2020-06-30 19:11 ` Arnd Bergmann
2020-07-01 10:16 ` [PATCH 02/18] compiler.h: Split {READ,WRITE}_ONCE " Will Deacon
2020-07-01 11:33 ` [PATCH 02/18] compiler.h: Split {READ, WRITE}_ONCE " Arnd Bergmann
2020-06-30 17:37 ` [PATCH 03/18] asm/rwonce: Allow __READ_ONCE to be overridden by the architecture Will Deacon
2020-06-30 17:37 ` [PATCH 04/18] alpha: Override READ_ONCE() with barriered implementation Will Deacon
2020-07-02 9:32 ` Mark Rutland
2020-07-02 9:48 ` Will Deacon
2020-07-02 10:08 ` Arnd Bergmann
2020-07-02 11:18 ` Will Deacon
2020-07-02 11:39 ` Arnd Bergmann
2020-07-02 14:43 ` Joel Fernandes
2020-07-02 14:55 ` Will Deacon
2020-07-02 15:07 ` Joel Fernandes
2020-06-30 17:37 ` [PATCH 05/18] asm/rwonce: Remove smp_read_barrier_depends() invocation Will Deacon
2020-06-30 17:37 ` [PATCH 06/18] vhost: Remove redundant use of read_barrier_depends() barrier Will Deacon
2020-06-30 17:37 ` [PATCH 07/18] alpha: Replace smp_read_barrier_depends() usage with smp_[r]mb() Will Deacon
2020-06-30 17:37 ` [PATCH 08/18] locking/barriers: Remove definitions for [smp_]read_barrier_depends() Will Deacon
2020-06-30 17:37 ` [PATCH 09/18] Documentation/barriers: Remove references to [smp_]read_barrier_depends() Will Deacon
2020-06-30 17:37 ` [PATCH 10/18] Documentation/barriers/kokr: " Will Deacon
2020-06-30 17:37 ` [PATCH 11/18] tools/memory-model: Remove smp_read_barrier_depends() from informal doc Will Deacon
2020-06-30 17:37 ` [PATCH 12/18] include/linux: Remove smp_read_barrier_depends() from comments Will Deacon
2020-06-30 17:37 ` [PATCH 13/18] checkpatch: Remove checks relating to [smp_]read_barrier_depends() Will Deacon
2020-06-30 17:37 ` [PATCH 14/18] arm64: Reduce the number of header files pulled into vmlinux.lds.S Will Deacon
2020-06-30 17:37 ` [PATCH 15/18] arm64: alternatives: Split up alternative.h Will Deacon
2020-06-30 17:37 ` [PATCH 16/18] arm64: cpufeatures: Add capability for LDAPR instruction Will Deacon
2020-06-30 17:37 ` [PATCH 17/18] arm64: alternatives: Remove READ_ONCE() usage during patch operation Will Deacon
2020-06-30 17:37 ` [PATCH 18/18] arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y Will Deacon
2020-06-30 19:25 ` Arnd Bergmann
2020-07-01 10:19 ` Will Deacon
2020-07-01 10:59 ` Arnd Bergmann
2020-06-30 19:47 ` Marco Elver
2020-06-30 20:20 ` Peter Zijlstra
2020-06-30 22:57 ` Sami Tolvanen
2020-07-01 10:25 ` Will Deacon
2020-07-01 10:24 ` Will Deacon
2020-07-01 17:07 ` Dave P Martin
2020-07-02 7:23 ` Will Deacon
2020-07-06 16:00 ` Dave Martin
2020-07-06 16:34 ` Paul E. McKenney
2020-07-06 17:05 ` Dave Martin
2020-07-06 17:36 ` Paul E. McKenney
2020-07-07 10:29 ` Dave Martin
2020-07-07 22:51 ` Paul E. McKenney
2020-07-07 23:01 ` Nick Desaulniers
2020-07-08 7:15 ` Marco Elver
2020-07-08 9:16 ` Peter Zijlstra
2020-07-08 18:20 ` Paul E. McKenney
2020-07-06 18:35 ` Will Deacon
2020-07-06 19:23 ` Marco Elver
2020-07-06 19:42 ` Paul E. McKenney
2020-07-06 16:08 ` Dave Martin [this message]
2020-07-06 18:35 ` Will Deacon
2020-07-07 10:10 ` Dave Martin
2020-07-01 7:38 ` [PATCH 00/18] Allow architectures to override __READ_ONCE() Josh Triplett
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