From: Will Deacon <will@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jinjie Ruan <ruanjinjie@huawei.com>,
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 13:48:23 +0100 [thread overview]
Message-ID: <agxcF1bzmErb_lB9@willie-the-truck> (raw)
In-Reply-To: <agIT0R4KV3YBYjlo@arm.com>
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?
Will
next prev parent reply other threads:[~2026-05-19 12:48 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 [this message]
2026-05-19 12:56 ` Jinjie Ruan
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