From nobody Sat Feb 7 21:14:37 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1EC1F30FF1C; Sun, 25 Jan 2026 22:49:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769381389; cv=none; b=qeCf9MpnqpTUBDzWMDWkJBkrFePVwyFdwPbWQ75aRPKNtipNMCwBYxa/Sxyd7EDyRDAsi886Xf/Sln/MQDgYqq6gpCohawPWq9k5xVzBBWGU6oFiwlb01j2INqmLwTBFCZJRxcs6yVNhzU7B8Fp6RIRiAphn8tCJ1VyjphYorZI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769381389; c=relaxed/simple; bh=8YH3jJJ1l+zWkUBN7W5HQtnoatv1adfZkeKPi8o8s7E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MRRnVGD8/s8oE4Z7PkRsV1wEXq72CWVMFD9NPsQthJCotl1EqWPsn73ZNkC5HSZF2hELUK7vnQAk5QVHYBd9cLjjr3QpQW66uJQLPR0ep5N7swnkJWxFBqnJ7wLLvrNGlb3y1f8mbDfyaUpakjF1WTiDt4kniqyYkr8YYAnSXFs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Xh9qasXM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Xh9qasXM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F034C19425; Sun, 25 Jan 2026 22:49:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769381388; bh=8YH3jJJ1l+zWkUBN7W5HQtnoatv1adfZkeKPi8o8s7E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Xh9qasXMZUMlZAvDOzubOT1QTX8nu9zdOSq/aG5SytkYO8dDUbUHJYFhPOhMIbOoc shv9P8Bht3wB1y2r2jVGvZJv0HRG80ck2wtcmqKvSpyaFC/xFWa1YeBCz4KK/9ivCR hYkK+Dyczy4RyH0t8DqAhfix9gdqot+5+jz0nhKl5oWWR6gbyqD0RRWpWeslUSffQg 5ffYgiOyzrLcj7I2oZeUcUBGC28h6CqUynsHVapP6lqi9yhKrLlwD6ZJaiFeb/Dw6q li4SD3zXYvOkkw7bhKz4ZGmz1nuunbm6XlRzlwkUldb6lKhtWEGk/kgzKSmleS680L XVtpddRKIJWYQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Andrew Morton , Bjorn Helgaas , Catalin Marinas , Chen Ridong , Danilo Krummrich , "David S . Miller" , Eric Dumazet , Gabriele Monaco , Greg Kroah-Hartman , Ingo Molnar , Jakub Kicinski , Jens Axboe , Johannes Weiner , Lai Jiangshan , Marco Crivellari , Michal Hocko , Muchun Song , Paolo Abeni , Peter Zijlstra , Phil Auld , "Rafael J . Wysocki" , Roman Gushchin , Shakeel Butt , Simon Horman , Tejun Heo , Thomas Gleixner , Vlastimil Babka , Waiman Long , Will Deacon , cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH 29/33] sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN Date: Sun, 25 Jan 2026 23:45:36 +0100 Message-ID: <20260125224541.50226-30-frederic@kernel.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20260125224541.50226-1-frederic@kernel.org> References: <20260125224541.50226-1-frederic@kernel.org> 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 Content-Type: text/plain; charset="utf-8" When none of the allowed CPUs of a task are online, it gets migrated to the fallback cpumask which is all the non nohz_full CPUs. However just like nohz_full CPUs, domain isolated CPUs don't want to be disturbed by tasks that have lost their CPU affinities. And since nohz_full rely on domain isolation to work correctly, the housekeeping mask of domain isolated CPUs should always be a subset of the housekeeping mask of nohz_full CPUs (there can be CPUs that are domain isolated but not nohz_full, OTOH there shouldn't be nohz_full CPUs that are not domain isolated): HK_TYPE_DOMAIN & HK_TYPE_KERNEL_NOISE =3D=3D HK_TYPE_DOMAIN Therefore use HK_TYPE_DOMAIN as the appropriate fallback target for tasks. Note that cpuset isolated partitions are not supported on those systems and may result in undefined behaviour. Signed-off-by: Frederic Weisbecker Reviewed-by: Waiman Long Acked-by: Will Deacon Tested-by: Will Deacon --- Documentation/arch/arm64/asymmetric-32bit.rst | 12 ++++++++---- arch/arm64/kernel/cpufeature.c | 6 +++--- 2 files changed, 11 insertions(+), 7 deletions(-) diff --git a/Documentation/arch/arm64/asymmetric-32bit.rst b/Documentation/= arch/arm64/asymmetric-32bit.rst index 57b8d7476f71..fc0c350c5e00 100644 --- a/Documentation/arch/arm64/asymmetric-32bit.rst +++ b/Documentation/arch/arm64/asymmetric-32bit.rst @@ -154,10 +154,14 @@ mode will return to host userspace with an ``exit_rea= son`` of ``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation. =20 -NOHZ FULL ---------- +SCHEDULER DOMAIN ISOLATION +-------------------------- =20 -To avoid perturbing an adaptive-ticks CPU (specified using -``nohz_full=3D``) when a 32-bit task is forcefully migrated, these CPUs +To avoid perturbing a boot-defined domain isolated CPU (specified using +``isolcpus=3D[domain]``) when a 32-bit task is forcefully migrated, these = CPUs are treated as 64-bit-only when support for asymmetric 32-bit systems is enabled. + +However as opposed to boot-defined domain isolation, runtime-defined domain +isolation using cpuset isolated partition is not advised on asymmetric +32-bit systems and will result in undefined behaviour. diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index c840a93b9ef9..f0e66cb27d17 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1669,7 +1669,7 @@ const struct cpumask *system_32bit_el0_cpumask(void) =20 const struct cpumask *task_cpu_fallback_mask(struct task_struct *p) { - return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_TICK)); + return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_DOMAIN)); } =20 static int __init parse_32bit_el0_param(char *str) @@ -3987,8 +3987,8 @@ static int enable_mismatched_32bit_el0(unsigned int c= pu) bool cpu_32bit =3D false; =20 if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) { - if (!housekeeping_cpu(cpu, HK_TYPE_TICK)) - pr_info("Treating adaptive-ticks CPU %u as 64-bit only\n", cpu); + if (!housekeeping_cpu(cpu, HK_TYPE_DOMAIN)) + pr_info("Treating domain isolated CPU %u as 64-bit only\n", cpu); else cpu_32bit =3D true; } --=20 2.51.1