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From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will@kernel.org>
Cc: Jann Horn <jannh@google.com>,
	kernel list <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	kernel-team <kernel-team@android.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Peter Oberparleiter <oberpar@linux.ibm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v4 07/11] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses
Date: Fri, 24 Apr 2020 19:43:34 +0200	[thread overview]
Message-ID: <20200424174334.GB13592@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200424171135.GJ21141@willie-the-truck>

On Fri, Apr 24, 2020 at 06:11:35PM +0100, Will Deacon wrote:
> My apologies, you're completely right. I thought that PAE mandated 64-bit
> atomicity, like it does on 32-bit ARM, but that's apparently not the case
> and looking at the 32-bit x86 pgtable code they have to be really careful
> there.

They added CMPXCHG8B for PAE, but then we never used it for that because
it's dead slow (MS did use it I think). Instead we play horrible split
word games, grep for CONFIG_GUP_GET_PTE_LOW_HIGH.

  reply	other threads:[~2020-04-24 17:44 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 15:15 [PATCH v4 00/11] Rework READ_ONCE() to improve codegen Will Deacon
2020-04-21 15:15 ` [PATCH v4 01/11] compiler/gcc: Raise minimum GCC version for kernel builds to 4.8 Will Deacon
2020-04-21 17:15   ` Masahiro Yamada
2020-04-21 15:15 ` [PATCH v4 02/11] netfilter: Avoid assigning 'const' pointer to non-const pointer Will Deacon
2020-04-21 15:15 ` [PATCH v4 03/11] net: tls: " Will Deacon
2020-04-21 15:15 ` [PATCH v4 04/11] fault_inject: Don't rely on "return value" from WRITE_ONCE() Will Deacon
2020-04-21 15:15 ` [PATCH v4 05/11] arm64: csum: Disable KASAN for do_csum() Will Deacon
2020-04-22  9:49   ` Mark Rutland
2020-04-22 10:41     ` Will Deacon
2020-04-22 11:01       ` Robin Murphy
2020-04-24  9:41         ` David Laight
2020-04-24 11:00           ` Robin Murphy
2020-04-24 13:04             ` David Laight
2020-04-21 15:15 ` [PATCH v4 06/11] READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE() Will Deacon
2020-04-22  9:51   ` Mark Rutland
2020-04-21 15:15 ` [PATCH v4 07/11] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses Will Deacon
2020-04-24 16:31   ` Jann Horn
2020-04-24 17:11     ` Will Deacon
2020-04-24 17:43       ` Peter Zijlstra [this message]
2020-04-21 15:15 ` [PATCH v4 08/11] READ_ONCE: Drop pointer qualifiers when reading from scalar types Will Deacon
2020-04-22 10:25   ` Rasmus Villemoes
2020-04-22 11:48     ` Segher Boessenkool
2020-04-22 13:11       ` Will Deacon
2020-04-22 14:54   ` Will Deacon
2020-04-21 15:15 ` [PATCH v4 09/11] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros Will Deacon
2020-04-21 15:15 ` [PATCH v4 10/11] arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros Will Deacon
2020-04-21 15:15 ` [PATCH v4 11/11] gcov: Remove old GCC 3.4 support Will Deacon
2020-04-21 17:19   ` Masahiro Yamada
2020-04-21 18:42 ` [PATCH v4 00/11] Rework READ_ONCE() to improve codegen Linus Torvalds
2020-04-22  8:18   ` Will Deacon
2020-04-22 11:37     ` Peter Zijlstra
2020-04-22 12:26       ` Will Deacon
2020-04-24 13:42         ` Will Deacon
2020-04-24 15:54           ` Marco Elver
2020-04-24 16:52             ` Will Deacon

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