From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: [PATCH 05/13] alpha: Override READ_ONCE() with barriered implementation Date: Fri, 8 Nov 2019 17:01:12 +0000 Message-ID: <20191108170120.22331-6-will@kernel.org> References: <20191108170120.22331-1-will@kernel.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573232506; bh=w1i4LnluNWu9HOrfPIIA9Bv7MDAafzVn7tCd1kalpQg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=R4GzqY7GaJ/tCwwOBuIgD/9Vjfa+xLyhA3XKsnAnsENVHus/GlmdMugS1pODMtR2B 93PYBj5mstl8jHY2pUuno4AE87iy55+/3X3/m+x7/kSJVKPiJNoE7NHRUOIFw3vi4I fw3iv4Nbn044CoL6uS5gBcEm/OQqbUpZsRRm87/U= In-Reply-To: <20191108170120.22331-1-will@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: linux-kernel@vger.kernel.org Cc: Will Deacon , Yunjae Lee , SeongJae Park , "Paul E. McKenney" , Josh Triplett , Matt Turner , Ivan Kokshaysky , Richard Henderson , Peter Zijlstra , Alan Stern , Michael Ellerman , "Michael S. Tsirkin" , Jason Wang , Arnd Bergmann , Joe Perches , Boqun Feng , linux-alpha@vger.kernel.org, virtualization@lists.linux-foundation.org Rather then relying on the core code to use 'smp_read_barrier_depends()' as part of the 'READ_ONCE()' definition, instead override 'READ_ONCE()' in the Alpha code so that it is treated the same way as 'smp_load_acquire()'. Signed-off-by: Will Deacon --- arch/alpha/include/asm/barrier.h | 61 ++++---------------------------- arch/alpha/include/asm/rwonce.h | 22 ++++++++++++ 2 files changed, 29 insertions(+), 54 deletions(-) create mode 100644 arch/alpha/include/asm/rwonce.h diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h index 92ec486a4f9e..1f6abe2d1392 100644 --- a/arch/alpha/include/asm/barrier.h +++ b/arch/alpha/include/asm/barrier.h @@ -2,64 +2,17 @@ #ifndef __BARRIER_H #define __BARRIER_H -#include - #define mb() __asm__ __volatile__("mb": : :"memory") #define rmb() __asm__ __volatile__("mb": : :"memory") #define wmb() __asm__ __volatile__("wmb": : :"memory") -/** - * read_barrier_depends - Flush all pending reads that subsequents reads - * depend on. - * - * No data-dependent reads from memory-like regions are ever reordered - * over this barrier. All reads preceding this primitive are guaranteed - * to access memory (but not necessarily other CPUs' caches) before any - * reads following this primitive that depend on the data return by - * any of the preceding reads. This primitive is much lighter weight than - * rmb() on most CPUs, and is never heavier weight than is - * rmb(). - * - * These ordering constraints are respected by both the local CPU - * and the compiler. - * - * Ordering is not guaranteed by anything other than these primitives, - * not even by data dependencies. See the documentation for - * memory_barrier() for examples and URLs to more information. - * - * For example, the following code would force ordering (the initial - * value of "a" is zero, "b" is one, and "p" is "&a"): - * - * - * CPU 0 CPU 1 - * - * b = 2; - * memory_barrier(); - * p = &b; q = p; - * read_barrier_depends(); - * d = *q; - * - * - * because the read of "*q" depends on the read of "p" and these - * two reads are separated by a read_barrier_depends(). However, - * the following code, with the same initial values for "a" and "b": - * - * - * CPU 0 CPU 1 - * - * a = 2; - * memory_barrier(); - * b = 3; y = b; - * read_barrier_depends(); - * x = a; - * - * - * does not enforce ordering, since there is no data dependency between - * the read of "a" and the read of "b". Therefore, on some CPUs, such - * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() - * in cases like this where there are no data dependencies. - */ -#define read_barrier_depends() __asm__ __volatile__("mb": : :"memory") +#define __smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = (*(volatile typeof(*p) *)(p)); \ + compiletime_assert_atomic_type(*p); \ + mb(); \ + ___p1; \ +}) #ifdef CONFIG_SMP #define __ASM_SMP_MB "\tmb\n" diff --git a/arch/alpha/include/asm/rwonce.h b/arch/alpha/include/asm/rwonce.h new file mode 100644 index 000000000000..ef5601352b55 --- /dev/null +++ b/arch/alpha/include/asm/rwonce.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2019 Google LLC. + */ +#ifndef __ASM_RWONCE_H +#define __ASM_RWONCE_H + +#include + +/* + * Alpha is apparently daft enough to reorder address-dependent loads + * on some CPU implementations. Knock some common sense into it with + * a memory barrier in READ_ONCE(). + */ +#define __read_once_size_1(p) __smp_load_acquire((u8 *)(p)) +#define __read_once_size_2(p) __smp_load_acquire((u16 *)(p)) +#define __read_once_size_4(p) __smp_load_acquire((u32 *)(p)) +#define __read_once_size_8(p) __smp_load_acquire((u64 *)(p)) + +#include + +#endif /* __ASM_RWONCE_H */ -- 2.24.0.rc1.363.gb1bccd3e3d-goog