From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A539A1CF7D5 for ; Mon, 15 Dec 2025 08:22:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765786958; cv=none; b=h51hOgeiFPWqm4DoO+5CNcct6Lu+LlXUMijqyk8qDm19UQZtZqqr4a6zpc3xdg0ouHPUb9svMB7ih6xnlf6C8Cy8lDrfCMUjVEBrQvD4dW+1Y81vQgewrwzTzWedRZm5iNbnNalgJjJe2TvwZDnbkl1KGXl4l4AICih7Ifg0n68= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765786958; c=relaxed/simple; bh=Hd84eTaanEcxZiV+PretsKZlnONdbdl93VYU6KWFius=; h=From:Subject:Date:Message-Id:MIME-Version:Content-Type:To:Cc; b=IK/Kcyf7nmm5Ar4NFXPTZAW1qIWvyxIUWPYOWysy0GvBMMUTPi6NrkcPI7zIiy8jKTVYuKJAeP8LPQbkIEdD6OJBe2YKzp+Nkr+QbCV0jLxYXr6SU4xIaJPm1LniVZs3u1gNFsSZN+amIqQ1aiq1q9/DQIaWjob+9cCBOVZHkGU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ekgsDF69; arc=none smtp.client-ip=95.215.58.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ekgsDF69" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1765786952; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=Y1K4zEPDRDMYMdi2xCl35yRWVX4/M4MCPPrB3uzXZsk=; b=ekgsDF69tdh7Uuq1rKl3gWMokZ9ARFJ2877cNabQluInZ5Tu/0yJYlIjIR9T6BqszVZv/H v61ZurDFpkvSjJNhVgqPPeaamS8XNngxrpkuTFRVY23cGQ+vm/+2o8jZUhqmN6fxj0cXB6 iEsa/Ao25PupjInA901b6SN/RxgIsaE= From: George Guo Subject: [PATCH v6 0/4] LoongArch: Add 128-bit atomic cmpxchg support (v5) Date: Mon, 15 Dec 2025 16:22:00 +0800 Message-Id: <20251215-2-v6-0-09a486e8df99@linux.dev> Precedence: bulk X-Mailing-List: loongarch@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIACjFP2kC/2XPwQ7CIAwG4FcxnMW0heL05HsYD2OAkphpNiUzZ u8u7CLR49/0+5u+xeiH6EexX73F4FMc463PwaxXoru0/dnL6HIWBMSIBJKkA9UYstQF40Teuw8 +xGnpOJ5yvsTxcRteS2XCMq11QglyC2xdpzUww+Ea++e0cT6JohPVQhdBWVjVEBpPHNzuV6ham CJUFg2j5ZbRNIC/Qn8FARehs/Dc2p3KfxH+3eBKIBXByx/aqjYwh62rxTzPHwuKubtaAQAA X-Change-ID: 20251120-2-d03862b2cf6d To: Huacai Chen , WANG Xuerui , hengqi.chen@gmail.com Cc: r@hev.cc, xry111@xry111.site, loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, George Guo , George Guo , Yangyang Lian X-Developer-Signature: v=1; a=ed25519-sha256; t=1765786949; l=3583; i=dongtai.guo@linux.dev; s=20251103; h=from:subject:message-id; bh=Hd84eTaanEcxZiV+PretsKZlnONdbdl93VYU6KWFius=; b=M3ywobYC3JlpKYqgxQ+tKybicVQNYN5Sql3Btgbv6BTi2/clYcWJRkbldrelIPUrRtbgWZU1w y6naFICV68IAdo57KFuh+blLvt8vsTQ+9Pei8yS5KyP1D/Hpn7/kZ94 X-Developer-Key: i=dongtai.guo@linux.dev; a=ed25519; pk=yHUJPGx/kAXutP/NSHpj7hWW0KQNlv3w9H6ju4qUoTM= X-Migadu-Flow: FLOW_OUT This patch series adds 128-bit atomic compare-and-exchange support for LoongArch architecture, which fixes BPF scheduler test failures caused by missing 128-bit atomics support. The series consists of four patches: 1. "LoongArch: Add SCQ support detection" - Check CPUCFG2_SCQ bit to determin if the CPU supports SCQ instrction. 2. "LoongArch: Add 128-bit atomic cmpxchg support" - Implements 128-bit atomic compare-and-exchange using LoongArch's LL.D/SC.Q instructions - Fixes BPF scheduler test failures (scx_central scx_qmap) where kmalloc_nolock_noprof returns NULL due to missing 128-bit atomics, leading to -ENOMEM errors during scheduler initialization 3. "LoongArch: Use spinlock to emulate 128-bit cmpxchg" - For LoongArch CPUs lacking 128-bit atomic instruction(e.g., the SCQ instruction on 3A5000), provide a fallback implementation of __cmpxchg128 using a spinlock to emulate the atomic operation. 4. "LoongArch: Enable 128-bit atomics cmpxchg support" - Adds select HAVE_CMPXCHG_DOUBLE and select HAVE_ALIGNED_STRUCT_PAGE in Kconfig to enable 128-bit atomic cmpxchg support The issue was identified through BPF scheduler test failures where scx_central and scx_qmap schedulers would fail to initialize. Testing was performed using the scx_qmap scheduler from tools/sched_ext/, confirming that the patches resolve the initialization failures. Signed-off-by: George Guo --- Changes in v6: - Put SCQ information in hwcap - Link to v5: https://lore.kernel.org/r/20251212-2-v5-0-704b3af55f7d@linux.dev Changes in v5: - Reordered the patches - Link to v4: https://lore.kernel.org/r/20251205-2-v4-0-e5ab932cf219@linux.dev Changes in v4: - Add SCQ support detection - Add spinlock to emulate 128-bit cmpxchg - Link to v3: https://lore.kernel.org/r/20251126-2-v3-0-851b5a516801@linux.dev Changes in v3: - dbar 0 -> __WEAK_LLSC_MB - =ZB" (__ptr[0]) -> "r" (__ptr) - Link to v2: https://lore.kernel.org/r/20251124-2-v2-0-b38216e25fd9@linux.dev Changes in v2: - Use a normal ld.d for the high word instead of ll.d to avoid race condition - Insert a dbar between ll.d and ld.d to prevent reordering - Simply __cmpxchg128_asm("ll.d", "sc.q", ptr, o, n) to __cmpxchg128_asm(ptr, o, n) - Fix address operand constraints after testing different approaches: * ld.d with "m" * ll.d with "ZC", * sc.q with "ZB"(alternative constraints caused issues: - "r" caused system hang - "ZC" caused compiler error: {standard input}: Assembler messages: {standard input}:10037: Fatal error: Immediate overflow. format: u0:0 ) - Link to v1: https://lore.kernel.org/r/20251120-2-v1-0-705bdc440550@linux.dev --- George Guo (4): LoongArch: Add SCQ support detection LoongArch: Add 128-bit atomic cmpxchg support LoongArch: Use spinlock to emulate 128-bit cmpxchg LoongArch: Enable 128-bit atomics cmpxchg support arch/loongarch/Kconfig | 2 + arch/loongarch/include/asm/cmpxchg.h | 66 +++++++++++++++++++++++++++++++ arch/loongarch/include/asm/cpu-features.h | 1 + arch/loongarch/include/asm/cpu.h | 2 + arch/loongarch/include/asm/loongarch.h | 1 + arch/loongarch/kernel/cpu-probe.c | 2 + arch/loongarch/kernel/proc.c | 1 + 7 files changed, 75 insertions(+) --- base-commit: 612df905d7404450696e979c806ba4cdef8684f4 change-id: 20251120-2-d03862b2cf6d Best regards, -- George Guo