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Date: Tue, 14 Mar 2017 10:53:36 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: Andy Lutomirski <luto@...capital.net>, Ingo Molnar <mingo@...nel.org>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
David Howells <dhowells@...hat.com>, Arnd Bergmann <arnd@...db.de>,
Al Viro <viro@...iv.linux.org.uk>, Dave Hansen <dave.hansen@...el.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook
<keescook@...omium.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Andy Lutomirski <luto@...nel.org>,
Ard Biesheuvel
<ard.biesheuvel@...aro.org>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Petr Mladek <pmladek@...e.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Helge Deller <deller@....de>, Rik van Riel <riel@...hat.com>,
John Stultz <john.stultz@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>, Oleg Nesterov <oleg@...hat.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>, Paolo Bonzini <pbonzini@...hat.com>,
Dmitry Safonov <dsafonov@...tuozzo.com>,
Borislav Petkov <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...hat.com>,
Brian Gerst <brgerst@...il.com>, Jan Beulich <JBeulich@...e.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Fenghua Yu <fenghua.yu@...el.com>, He Chen <he.chen@...ux.intel.com>,
Russell King <linux@...linux.org.uk>,
Vladimir Murzin <vladimir.murzin@....com>,
Will Deacon
<will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>, James Morse <james.morse@....com>,
"David A . Long" <dave.long@...aro.org>,
Pratyush Anand <panand@...hat.com>, Laura Abbott <labbott@...hat.com>,
Andre Przywara <andre.przywara@....com>,
Chris Metcalf <cmetcalf@...lanox.com>,
linux-s390 <linux-s390@...r.kernel.org>,
LKML
<linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 2/4] x86/syscalls: Specific usage of
verify_pre_usermode_state
On 03/14/17 09:51, Thomas Garnier wrote:
>>
>> I wanted to comment on that thing: why on earth isn't
>> verify_pre_usermode_state() an inline? Making it an out-of-line
>> function adds pointless extra overhead to the C code when we are talking
>> about a few instructions.
>
> Because outside of arch specific implementation it is called by each
> syscall handler. it will increase the code size a lot.
>
Don't assume that. On a lot of architectures a function call can be
more expensive than a simple compare and branch, because the compiler
has to assume a whole bunch of registers are lost at that point.
Either way, don't penalize the common architectures for it. Not okay.
-hpa
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