From: Will Deacon <will@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
Kees Cook <keescook@chromium.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Sami Tolvanen <samitolvanen@google.com>,
Masahiro Yamada <masahiroy@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 4/4] arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y
Date: Tue, 3 Nov 2020 13:13:29 +0000 [thread overview]
Message-ID: <20201103131328.GC5219@willie-the-truck> (raw)
In-Reply-To: <20201103125845.GD40454@C02TD0UTHF1T.local>
On Tue, Nov 03, 2020 at 12:58:45PM +0000, Mark Rutland wrote:
> On Tue, Nov 03, 2020 at 12:17:21PM +0000, 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.
> >
> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Will Deacon <will@kernel.org>
>
> [...]
>
> Could we add a note above __READ_ONCE() along the lines of the commit
> message, e.g.
>
> /*
> * With LTO a compiler might convert an address dependency headed by a
> * READ_ONCE() into a control dependency, allowing for harmful
> * reordering by the CPU.
> *
> * To prevent this, upgrade READ_OONCE() to provide acquire semantics
> * when building with LTO.
It's not halloween any moooore :)
But yes, I'll add something to that effect, cheers.
Will
next prev parent reply other threads:[~2020-11-03 13:13 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-03 12:17 [PATCH v4 0/4] Upgrade READ_ONCE() to RCpc acquire on arm64 with LTO Will Deacon
2020-11-03 12:17 ` [PATCH v4 1/4] arm64: alternatives: Split up alternative.h Will Deacon
2020-11-03 12:40 ` Mark Rutland
2020-11-03 12:42 ` Will Deacon
2020-11-03 12:17 ` [PATCH v4 2/4] arm64: cpufeatures: Add capability for LDAPR instruction Will Deacon
2020-11-03 12:44 ` Mark Rutland
2020-11-03 12:17 ` [PATCH v4 3/4] arm64: alternatives: Remove READ_ONCE() usage during patch operation Will Deacon
2020-11-03 12:46 ` Mark Rutland
2020-11-03 12:17 ` [PATCH v4 4/4] arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y Will Deacon
2020-11-03 12:58 ` Mark Rutland
2020-11-03 13:13 ` Will Deacon [this message]
2020-11-09 23:25 ` [PATCH v4 0/4] Upgrade READ_ONCE() to RCpc acquire on arm64 with LTO Will Deacon
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