From nobody Sun Feb 8 15:29:14 2026 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 CAC692F3612 for ; Wed, 31 Dec 2025 03:45:36 +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=1767152739; cv=none; b=bLYcRQA/aCAtRHLGg6ykSb6HlB01etsSkc6nTFfRzWwte3ItsIU3iAaz0gsGdOWoTvR5pKoaTvKGDNqWwqMDnleDpffGzngRPNFTFeBkwA4/OmnZFI1SFXKpHEEJccJBjitK1IvQRB98YX7LdJ3Z7/avjzHGhlC1tGisYhJ7ADs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767152739; c=relaxed/simple; bh=PkouoUlrstxq/7OVZRdcZvNPKO5ZYSIi/obW6WYAxJg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ApJtVMMtZuVpBxtp1VSIAZ1tahNpPKsiRkBE5i3yLqWWVik5le/1gEzuA3o7uQ20efFURVxmtjhXq7hmZFOkZAAVfco86NWmvUN5f61R7w11fIs3PwUZ/68dRPom4xEhYa93ULbeOZJaF3pc5FA/O+yrmXE0MKZFj6OAfOacelM= 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=YlqKW2YP; 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="YlqKW2YP" 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=1767152735; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KwyqUC0qz/7HldbWplcKPTskOM2D1bC7Y9+f+VDp2yQ=; b=YlqKW2YPFXzP/NfHxUOCvdS2e+rAjnJnUuMJi4qW94ixhcmbHZ6qcjieZ2On6ev/83H4hu ODgo7lArJnU/6KCUJO+c0qgDknwj5NPtFpSJcWDkLxW7LiAyqJD1JUeFJ+xbB0t8gdpdNz CqMAeVCwjFaUWH7DUjbC6ZVFO7fudhE= From: George Guo To: hengqi.chen@gmail.com Cc: chenhuacai@kernel.org, dongtai.guo@linux.dev, guodongtai@kylinos.cn, kernel@xen0n.name, lianyangyang@kylinos.cn, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, r@hev.cc, xry111@xry111.site Subject: [PATCH v8 loongarch-next 2/3] LoongArch: Add 128-bit atomic cmpxchg support Date: Wed, 31 Dec 2025 11:45:22 +0800 Message-ID: <20251231034523.47014-3-dongtai.guo@linux.dev> In-Reply-To: <20251231034523.47014-1-dongtai.guo@linux.dev> References: <20251231034523.47014-1-dongtai.guo@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" From: George Guo Implement 128-bit atomic compare-and-exchange using LoongArch's LL.D/SC.Q instructions. For LoongArch CPUs lacking 128-bit atomic instruction(e.g., the SCQ instruction on 3A5000), use a spinlock to emulate the atomic operation. At the same time, fix BPF scheduler test failures (scx_central scx_qmap) caused by kmalloc_nolock_noprof returning NULL due to missing 128-bit atomics. The NULL returns led to -ENOMEM errors during scheduler initialization, causing test cases to fail. Verified by testing with the scx_qmap scheduler (located in tools/sched_ext/). Building with `make` and running ./tools/sched_ext/build/bin/scx_qmap. Link: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?i= d=3D5fb750e8a9ae Signed-off-by: George Guo Acked-by: Hengqi Chen Tested-by: Hengqi Chen --- arch/loongarch/include/asm/cmpxchg.h | 66 ++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) diff --git a/arch/loongarch/include/asm/cmpxchg.h b/arch/loongarch/include/= asm/cmpxchg.h index 0494c2ab553e..ef793bcb7b25 100644 --- a/arch/loongarch/include/asm/cmpxchg.h +++ b/arch/loongarch/include/asm/cmpxchg.h @@ -8,6 +8,7 @@ #include #include #include +#include =20 #define __xchg_amo_asm(amswap_db, m, val) \ ({ \ @@ -137,6 +138,61 @@ __arch_xchg(volatile void *ptr, unsigned long x, int s= ize) __ret; \ }) =20 +union __u128_halves { + u128 full; + struct { + u64 low; + u64 high; + }; +}; + +#define __cmpxchg128_asm(ptr, old, new) \ +({ \ + union __u128_halves __old, __new, __ret; \ + volatile u64 *__ptr =3D (volatile u64 *)(ptr); \ + \ + __old.full =3D (old); \ + __new.full =3D (new); \ + \ + __asm__ __volatile__( \ + "1: ll.d %0, %3 # 128-bit cmpxchg low \n" \ + __WEAK_LLSC_MB \ + " ld.d %1, %4 # 128-bit cmpxchg high \n" \ + " bne %0, %z5, 2f \n" \ + " bne %1, %z6, 2f \n" \ + " move $t0, %z7 \n" \ + " move $t1, %z8 \n" \ + " sc.q $t0, $t1, %2 \n" \ + " beqz $t0, 1b \n" \ + "2: \n" \ + __WEAK_LLSC_MB \ + : "=3D&r" (__ret.low), "=3D&r" (__ret.high) \ + : "r" (__ptr), \ + "ZC" (__ptr[0]), "m" (__ptr[1]), \ + "Jr" (__old.low), "Jr" (__old.high), \ + "Jr" (__new.low), "Jr" (__new.high) \ + : "t0", "t1", "memory"); \ + \ + __ret.full; \ +}) + +#define __cmpxchg128_locked(ptr, old, new) \ +({ \ + u128 __ret; \ + static DEFINE_SPINLOCK(lock); \ + unsigned long flags; \ + \ + spin_lock_irqsave(&lock, flags); \ + \ + __ret =3D *(volatile u128 *)(ptr); \ + if (__ret =3D=3D (old)) \ + *(volatile u128 *)(ptr) =3D (new); \ + \ + spin_unlock_irqrestore(&lock, flags); \ + \ + __ret; \ +}) + static inline unsigned int __cmpxchg_small(volatile void *ptr, unsigned in= t old, unsigned int new, unsigned int size) { @@ -224,6 +280,16 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsig= ned long new, unsigned int __res; \ }) =20 +/* cmpxchg128 */ +#define system_has_cmpxchg128() 1 + +#define arch_cmpxchg128(ptr, o, n) \ +({ \ + BUILD_BUG_ON(sizeof(*(ptr)) !=3D 16); \ + cpu_has_scq ? __cmpxchg128_asm(ptr, o, n) : \ + __cmpxchg128_locked(ptr, o, n); \ +}) + #ifdef CONFIG_64BIT #define arch_cmpxchg64_local(ptr, o, n) \ ({ \ --=20 2.49.0