From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E898C3DA78 for ; Sat, 14 Jan 2023 09:53:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230140AbjANJxH (ORCPT ); Sat, 14 Jan 2023 04:53:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230149AbjANJxH (ORCPT ); Sat, 14 Jan 2023 04:53:07 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 628A5A2 for ; Sat, 14 Jan 2023 01:53:05 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 000B160765 for ; Sat, 14 Jan 2023 09:53:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBD15C433D2; Sat, 14 Jan 2023 09:53:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1673689984; bh=PmEubvVaMqjZ47dGJDB3/J8uxmk+DQ16jQX3PFGRuhY=; h=Subject:To:Cc:From:Date:From; b=nEgeXg1B6V0YdA3A9frVemfw7K167lty7IRKzzchrUZjS+rPuRyooy16ExQFS9uUc OKdWYkkJ8e6R3sSUDaUlZNr3F5/vtnxQN+UT01SU5ArTvUe9TltXgP0w/+e5VNbF5i flIDEc/2Z/31WSy6oSqmc9ewECZHPscjYkgs3554= Subject: FAILED: patch "[PATCH] arm64: cmpxchg_double*: hazard against entire exchange" failed to apply to 4.19-stable tree To: mark.rutland@arm.com, arnd@arndb.de, boqun.feng@gmail.com, catalin.marinas@arm.com, peterz@infradead.org, steve.capper@arm.com, will@kernel.org Cc: From: Date: Sat, 14 Jan 2023 10:53:01 +0100 Message-ID: <1673689981394@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . Possible dependencies: 031af50045ea ("arm64: cmpxchg_double*: hazard against entire exchange variable") b2c3ccbd0011 ("arm64: atomics: remove LL/SC trampolines") 8e6082e94aac ("arm64: atomics: format whitespace consistently") 4f6cdf296cc4 ("Merge branches 'for-next/acpi', 'for-next/cpufeatures', 'for-next/csum', 'for-next/e0pd', 'for-next/entry', 'for-next/kbuild', 'for-next/kexec/cleanup', 'for-next/kexec/file-kdump', 'for-next/misc', 'for-next/nofpsimd', 'for-next/perf' and 'for-next/scs' into for-next/core") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 031af50045ea97ed4386eb3751ca2c134d0fc911 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Wed, 4 Jan 2023 15:16:26 +0000 Subject: [PATCH] arm64: cmpxchg_double*: hazard against entire exchange variable The inline assembly for arm64's cmpxchg_double*() implementations use a +Q constraint to hazard against other accesses to the memory location being exchanged. However, the pointer passed to the constraint is a pointer to unsigned long, and thus the hazard only applies to the first 8 bytes of the location. GCC can take advantage of this, assuming that other portions of the location are unchanged, leading to a number of potential problems. This is similar to what we fixed back in commit: fee960bed5e857eb ("arm64: xchg: hazard against entire exchange variable") ... but we forgot to adjust cmpxchg_double*() similarly at the same time. The same problem applies, as demonstrated with the following test: | struct big { | u64 lo, hi; | } __aligned(128); | | unsigned long foo(struct big *b) | { | u64 hi_old, hi_new; | | hi_old = b->hi; | cmpxchg_double_local(&b->lo, &b->hi, 0x12, 0x34, 0x56, 0x78); | hi_new = b->hi; | | return hi_old ^ hi_new; | } ... which GCC 12.1.0 compiles as: | 0000000000000000 : | 0: d503233f paciasp | 4: aa0003e4 mov x4, x0 | 8: 1400000e b 40 | c: d2800240 mov x0, #0x12 // #18 | 10: d2800681 mov x1, #0x34 // #52 | 14: aa0003e5 mov x5, x0 | 18: aa0103e6 mov x6, x1 | 1c: d2800ac2 mov x2, #0x56 // #86 | 20: d2800f03 mov x3, #0x78 // #120 | 24: 48207c82 casp x0, x1, x2, x3, [x4] | 28: ca050000 eor x0, x0, x5 | 2c: ca060021 eor x1, x1, x6 | 30: aa010000 orr x0, x0, x1 | 34: d2800000 mov x0, #0x0 // #0 <--- BANG | 38: d50323bf autiasp | 3c: d65f03c0 ret | 40: d2800240 mov x0, #0x12 // #18 | 44: d2800681 mov x1, #0x34 // #52 | 48: d2800ac2 mov x2, #0x56 // #86 | 4c: d2800f03 mov x3, #0x78 // #120 | 50: f9800091 prfm pstl1strm, [x4] | 54: c87f1885 ldxp x5, x6, [x4] | 58: ca0000a5 eor x5, x5, x0 | 5c: ca0100c6 eor x6, x6, x1 | 60: aa0600a6 orr x6, x5, x6 | 64: b5000066 cbnz x6, 70 | 68: c8250c82 stxp w5, x2, x3, [x4] | 6c: 35ffff45 cbnz w5, 54 | 70: d2800000 mov x0, #0x0 // #0 <--- BANG | 74: d50323bf autiasp | 78: d65f03c0 ret Notice that at the lines with "BANG" comments, GCC has assumed that the higher 8 bytes are unchanged by the cmpxchg_double() call, and that `hi_old ^ hi_new` can be reduced to a constant zero, for both LSE and LL/SC versions of cmpxchg_double(). This patch fixes the issue by passing a pointer to __uint128_t into the +Q constraint, ensuring that the compiler hazards against the entire 16 bytes being modified. With this change, GCC 12.1.0 compiles the above test as: | 0000000000000000 : | 0: f9400407 ldr x7, [x0, #8] | 4: d503233f paciasp | 8: aa0003e4 mov x4, x0 | c: 1400000f b 48 | 10: d2800240 mov x0, #0x12 // #18 | 14: d2800681 mov x1, #0x34 // #52 | 18: aa0003e5 mov x5, x0 | 1c: aa0103e6 mov x6, x1 | 20: d2800ac2 mov x2, #0x56 // #86 | 24: d2800f03 mov x3, #0x78 // #120 | 28: 48207c82 casp x0, x1, x2, x3, [x4] | 2c: ca050000 eor x0, x0, x5 | 30: ca060021 eor x1, x1, x6 | 34: aa010000 orr x0, x0, x1 | 38: f9400480 ldr x0, [x4, #8] | 3c: d50323bf autiasp | 40: ca0000e0 eor x0, x7, x0 | 44: d65f03c0 ret | 48: d2800240 mov x0, #0x12 // #18 | 4c: d2800681 mov x1, #0x34 // #52 | 50: d2800ac2 mov x2, #0x56 // #86 | 54: d2800f03 mov x3, #0x78 // #120 | 58: f9800091 prfm pstl1strm, [x4] | 5c: c87f1885 ldxp x5, x6, [x4] | 60: ca0000a5 eor x5, x5, x0 | 64: ca0100c6 eor x6, x6, x1 | 68: aa0600a6 orr x6, x5, x6 | 6c: b5000066 cbnz x6, 78 | 70: c8250c82 stxp w5, x2, x3, [x4] | 74: 35ffff45 cbnz w5, 5c | 78: f9400480 ldr x0, [x4, #8] | 7c: d50323bf autiasp | 80: ca0000e0 eor x0, x7, x0 | 84: d65f03c0 ret ... sampling the high 8 bytes before and after the cmpxchg, and performing an EOR, as we'd expect. For backporting, I've tested this atop linux-4.9.y with GCC 5.5.0. Note that linux-4.9.y is oldest currently supported stable release, and mandates GCC 5.1+. Unfortunately I couldn't get a GCC 5.1 binary to run on my machines due to library incompatibilities. I've also used a standalone test to check that we can use a __uint128_t pointer in a +Q constraint at least as far back as GCC 4.8.5 and LLVM 3.9.1. Fixes: 5284e1b4bc8a ("arm64: xchg: Implement cmpxchg_double") Fixes: e9a4b795652f ("arm64: cmpxchg_dbl: patch in lse instructions when supported by the CPU") Reported-by: Boqun Feng Link: https://lore.kernel.org/lkml/Y6DEfQXymYVgL3oJ@boqun-archlinux/ Reported-by: Peter Zijlstra Link: https://lore.kernel.org/lkml/Y6GXoO4qmH9OIZ5Q@hirez.programming.kicks-ass.net/ Signed-off-by: Mark Rutland Cc: stable@vger.kernel.org Cc: Arnd Bergmann Cc: Catalin Marinas Cc: Steve Capper Cc: Will Deacon Link: https://lore.kernel.org/r/20230104151626.3262137-1-mark.rutland@arm.com Signed-off-by: Will Deacon diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h index 0890e4f568fb..cbb3d961123b 100644 --- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h @@ -315,7 +315,7 @@ __ll_sc__cmpxchg_double##name(unsigned long old1, \ " cbnz %w0, 1b\n" \ " " #mb "\n" \ "2:" \ - : "=&r" (tmp), "=&r" (ret), "+Q" (*(unsigned long *)ptr) \ + : "=&r" (tmp), "=&r" (ret), "+Q" (*(__uint128_t *)ptr) \ : "r" (old1), "r" (old2), "r" (new1), "r" (new2) \ : cl); \ \ diff --git a/arch/arm64/include/asm/atomic_lse.h b/arch/arm64/include/asm/atomic_lse.h index 52075e93de6c..a94d6dacc029 100644 --- a/arch/arm64/include/asm/atomic_lse.h +++ b/arch/arm64/include/asm/atomic_lse.h @@ -311,7 +311,7 @@ __lse__cmpxchg_double##name(unsigned long old1, \ " eor %[old2], %[old2], %[oldval2]\n" \ " orr %[old1], %[old1], %[old2]" \ : [old1] "+&r" (x0), [old2] "+&r" (x1), \ - [v] "+Q" (*(unsigned long *)ptr) \ + [v] "+Q" (*(__uint128_t *)ptr) \ : [new1] "r" (x2), [new2] "r" (x3), [ptr] "r" (x4), \ [oldval1] "r" (oldval1), [oldval2] "r" (oldval2) \ : cl); \