arm64: Add HOTPLUG_PARALLEL support for secondary CPUs [LWN.net]

From:		Jinjie Ruan <ruanjinjie-AT-huawei.com>
To:		<catalin.marinas-AT-arm.com>, <will-AT-kernel.org>, <tsbogend-AT-alpha.franken.de>, <pjw-AT-kernel.org>, <palmer-AT-dabbelt.com>, <aou-AT-eecs.berkeley.edu>, <alex-AT-ghiti.fr>, <tglx-AT-kernel.org>, <mingo-AT-redhat.com>, <bp-AT-alien8.de>, <dave.hansen-AT-linux.intel.com>, <hpa-AT-zytor.com>, <peterz-AT-infradead.org>, <kees-AT-kernel.org>, <nathan-AT-kernel.org>, <linusw-AT-kernel.org>, <jpoimboe-AT-kernel.org>, <lukas.bulwahn-AT-redhat.com>, <ryan.roberts-AT-arm.com>, <ojeda-AT-kernel.org>, <maz-AT-kernel.org>, <timothy.hayes-AT-arm.com>, <lpieralisi-AT-kernel.org>, <thuth-AT-redhat.com>, <menglong8.dong-AT-gmail.com>, <oupton-AT-kernel.org>, <yeoreum.yun-AT-arm.com>, <miko.lenczewski-AT-arm.com>, <broonie-AT-kernel.org>, <kevin.brodsky-AT-arm.com>, <james.clark-AT-linaro.org>, <tabba-AT-google.com>, <mrigendra.chaubey-AT-gmail.com>, <arnd-AT-arndb.de>, <anshuman.khandual-AT-arm.com>, <x86-AT-kernel.org>, <linux-kernel-AT-vger.kernel.org>, <linux-arm-kernel-AT-lists.infradead.org>, <linux-mips-AT-vger.kernel.org>, <linux-riscv-AT-lists.infradead.org>, <apatel-AT-ventanamicro.com>, <mhklinux-AT-outlook.com>
Subject:		[PATCH v2 0/4] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs
Date:		Thu, 18 Jun 2026 17:24:40 +0800
Message-ID:		<20260618092444.1316336-1-ruanjinjie@huawei.com>
Cc:		<ruanjinjie-AT-huawei.com>
Archive-link:		Article

Support for parallel secondary CPU bringup is already utilized by x86,
MIPS, and RISC-V. This patch brings this capability to the arm64
architecture.

Introduce CONFIG_PARALLEL_SMT_PRIMARY_FIRST to avoid primary SMT threads
to boot first constraint.

And Add a 'cpu' parameter to update_cpu_boot_status() to allow updating the
boot status at a per-CPU granularity during parallel bringup.

Rework the global `secondary_data` accessed during early boot into
a per-CPU array `cpu_boot_data` to allow secondary CPUs to boot
in parallel.

And reuse `__cpu_logical_map` array in the early boot code in head.S
to resolve each secondary CPU's logical ID concurrently.

Changes in v2:
- Remove RFC.
- Add Tested-by.
- Fix AI review issues in [1].
- Add arch_cpuhp_init_parallel_bringup() to check psci boot.
- Reuse `__cpu_logical_map` instead of a new aray.
- Defer rcutree_report_cpu_starting() until after
  check_local_cpu_capabilities() to prevent a potential control CPU
  deadlock if an early capability check fails.
- Move the assembly in head.S to a macro called `mpidr_to_cpuid`.
- Add `SECONDARY_DATA_SHIFT` for `lsl` to access `cpu_boot_data`.
- Add sizeof(struct secondary_data) power of 2 assert check.
- Expand testing with more data collected from real hardware.

[1] https://sashiko.dev/#/patchset/20260611133809.3854977-1-r...

Jinjie Ruan (4):
  cpu/hotplug: Introduce CONFIG_PARALLEL_SMT_PRIMARY_FIRST
  arm64: smp: Pass CPU ID to update_cpu_boot_status()
  arm64: smp: Defer RCU reporting until after local CPU capability
    checks
  arm64: Add HOTPLUG_PARALLEL support for secondary CPUs

 arch/Kconfig                    |  4 +++
 arch/arm64/Kconfig              |  1 +
 arch/arm64/include/asm/smp.h    | 17 ++++++++++---
 arch/arm64/kernel/asm-offsets.c |  4 +++
 arch/arm64/kernel/cpufeature.c  | 22 ++++++++--------
 arch/arm64/kernel/head.S        | 36 ++++++++++++++++++++++++++
 arch/arm64/kernel/smp.c         | 45 ++++++++++++++++++++++++++++-----
 arch/arm64/mm/context.c         |  4 +--
 arch/mips/Kconfig               |  1 +
 arch/riscv/Kconfig              |  1 +
 arch/x86/Kconfig                |  1 +
 kernel/cpu.c                    |  6 ++++-
 12 files changed, 119 insertions(+), 23 deletions(-)

-- 
2.34.1