From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 577746B0009 for ; Mon, 29 Jan 2018 12:30:30 -0500 (EST) Received: by mail-wr0-f198.google.com with SMTP id d14so6170768wre.6 for ; Mon, 29 Jan 2018 09:30:30 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id r128sor3021947wmg.85.2018.01.29.09.30.28 for (Google Transport Security); Mon, 29 Jan 2018 09:30:29 -0800 (PST) From: Dmitry Vyukov Subject: [PATCH v6 4/4] asm-generic, x86: add comments for atomic instrumentation Date: Mon, 29 Jan 2018 18:26:07 +0100 Message-Id: In-Reply-To: References: In-Reply-To: References: Sender: owner-linux-mm@kvack.org List-ID: To: mark.rutland@arm.com, peterz@infradead.org, mingo@redhat.com, will.deacon@arm.com, hpa@zytor.com, aryabinin@virtuozzo.com, kasan-dev@googlegroups.com, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de Cc: Dmitry Vyukov , Andrew Morton , linux-mm@kvack.org The comments are factored out from the code changes to make them easier to read. Add them separately to explain some non-obvious aspects. Signed-off-by: Dmitry Vyukov Cc: Mark Rutland Cc: Peter Zijlstra Cc: Will Deacon Cc: Andrew Morton Cc: Andrey Ryabinin Cc: Ingo Molnar Cc: kasan-dev@googlegroups.com Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: x86@kernel.org --- Changes since v3: - rephrase comment in arch_atomic_read() Changes since v5: - remove comment explaining cmpxchg macro mess, since we don't have the mess now. --- arch/x86/include/asm/atomic.h | 4 ++++ include/asm-generic/atomic-instrumented.h | 21 +++++++++++++++++++++ 2 files changed, 25 insertions(+) diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h index 33afc966d6a9..0db6bec95489 100644 --- a/arch/x86/include/asm/atomic.h +++ b/arch/x86/include/asm/atomic.h @@ -24,6 +24,10 @@ */ static __always_inline int arch_atomic_read(const atomic_t *v) { + /* + * Note for KASAN: we deliberately don't use READ_ONCE_NOCHECK() here, + * it's non-inlined function that increases binary size and stack usage. + */ return READ_ONCE((v)->counter); } diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h index 82e080505982..ec07f23678ea 100644 --- a/include/asm-generic/atomic-instrumented.h +++ b/include/asm-generic/atomic-instrumented.h @@ -1,3 +1,15 @@ +/* + * This file provides wrappers with KASAN instrumentation for atomic operations. + * To use this functionality an arch's atomic.h file needs to define all + * atomic operations with arch_ prefix (e.g. arch_atomic_read()) and include + * this file at the end. This file provides atomic_read() that forwards to + * arch_atomic_read() for actual atomic operation. + * Note: if an arch atomic operation is implemented by means of other atomic + * operations (e.g. atomic_read()/atomic_cmpxchg() loop), then it needs to use + * arch_ variants (i.e. arch_atomic_read()/arch_atomic_cmpxchg()) to avoid + * double instrumentation. + */ + #ifndef _LINUX_ATOMIC_INSTRUMENTED_H #define _LINUX_ATOMIC_INSTRUMENTED_H @@ -442,6 +454,15 @@ cmpxchg64_local_size(volatile u64 *ptr, u64 old, u64 new) (u64)(new))); \ }) +/* + * Originally we had the following code here: + * __typeof__(p1) ____p1 = (p1); + * kasan_check_write(____p1, 2 * sizeof(*____p1)); + * arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2)); + * But it leads to compilation failures (see gcc issue 72873). + * So for now it's left non-instrumented. + * There are few callers of cmpxchg_double(), so it's not critical. + */ #define cmpxchg_double(p1, p2, o1, o2, n1, n2) \ ({ \ arch_cmpxchg_double((p1), (p2), (o1), (o2), (n1), (n2)); \ -- 2.16.0.rc1.238.g530d649a79-goog -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org