From: Jinjie Ruan <ruanjinjie@huawei.com>
To: Will Deacon <will@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>
Cc: <punit.agrawal@oss.qualcomm.com>, <rafael.j.wysocki@intel.com>,
<fengchengwen@huawei.com>, <chenl311@chinatelecom.cn>,
<suzuki.poulose@arm.com>, <maz@kernel.org>,
<timothy.hayes@arm.com>, <lpieralisi@kernel.org>,
<mrigendra.chaubey@gmail.com>, <arnd@arndb.de>,
<sudeep.holla@kernel.org>, <yangyicong@hisilicon.com>,
<jic23@kernel.org>, <pierre.gondois@arm.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <james.morse@arm.com>
Subject: Re: [PATCH v2] cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()
Date: Tue, 19 May 2026 20:56:18 +0800 [thread overview]
Message-ID: <0079639f-5ea4-4aea-b002-e13750f87d87@huawei.com> (raw)
In-Reply-To: <agxcF1bzmErb_lB9@willie-the-truck>
On 5/19/2026 8:48 PM, Will Deacon wrote:
> On Mon, May 11, 2026 at 06:37:21PM +0100, Catalin Marinas wrote:
>> On Mon, Apr 27, 2026 at 10:35:07AM +0800, Jinjie Ruan wrote:
>>> On arm64, when booting with `maxcpus` greater than the number of present
>>> CPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present'
>>> but have not yet been registered via register_cpu(). Consequently,
>>> the per-cpu device objects for these CPUs are not yet initialized.
>> [...]
>>> Fix this by:
>>>
>>> 1. When booting with ACPI, checking the ACPI_MADT_ENABLED flag in the GICC
>>> entry before calling set_cpu_present() during SMP initialization.
>>>
>>> 2. Properly managing the present mask in acpi_map_cpu() and
>>> acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with
>>> other architectures like x86 and LoongArch.
>>
>> I had a chat with James earlier and IIUC the decision was to mark all
>> CPUs present and the GIC must be fully initialised. But digging through
>> the GICv3 code, I don't see it depending on cpu_present_mask but rather
>> on the "always on" MADT GICR description. So I think it should be safe
>> as long as we don't rely on the GICC gicr_base_address. But we should
>> update Documentation/arch/arm64/cpu-hotplug.rst to no longer state that
>> all online-capable vCPUs are marked as present by the kernel.
>>
>> (or maybe I misunderstood all this)
>
> Jinjie, do you plan to respin with a documentation update as per
> Catalin's comment above?
Ah, sorry, I will definitely include this change in the next version soon.
Thanks,
Jinjie
>
> Will
>
prev parent reply other threads:[~2026-05-19 12:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 2:35 [PATCH v2] cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable() Jinjie Ruan
2026-05-11 3:17 ` Jinjie Ruan
2026-05-11 9:55 ` Catalin Marinas
2026-05-11 17:37 ` Catalin Marinas
2026-05-19 12:48 ` Will Deacon
2026-05-19 12:56 ` Jinjie Ruan [this message]
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