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Message-ID: <CAGXu5jLFAOhs0eak9BfNP=3XLwtHxdSqNF+AB_yjcWyX1=SoNQ@mail.gmail.com>
Date: Wed, 26 Jul 2017 21:16:10 -0700
From: Kees Cook <keescook@...omium.org>
To: Li Kun <hw.likun@...wei.com>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>, Mark Rutland <mark.rutland@....com>,
Laura Abbott <labbott@...oraproject.org>, Will Deacon <will.deacon@....com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2] arm64: kernel: implement fast refcount checking
On Wed, Jul 26, 2017 at 7:11 PM, Li Kun <hw.likun@...wei.com> wrote:
> @Kees, should we implement the add-from-zero case ? What do you think?
If it can be done efficiently, yes. In the x86 case, it would
basically change "lock inc" into a huge cmpxchg loop, and it almost
doubled the cycles for the operation. Since
refcount_inc()/refcount_dec_and_test() is the primary code pattern,
it's not a good idea to mess with performance on especially those.
This LKDTM series should provide a good perf target to compare
against:
https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=lkdtm/refcount
-Kees
--
Kees Cook
Pixel Security
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