[PATCH v3 00/12] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs

[Will Deacon]

On Tue, Jul 07, 2026 at 04:14:06PM +0800, Jinjie Ruan wrote:
> 
> 
> On 7/7/2026 1:39 AM, Will Deacon wrote:
> > Hi Jinjie,
> > 
> > On Thu, Jun 25, 2026 at 09:34:36AM +0800, Jinjie Ruan wrote:
> >> On 6/24/2026 8:16 PM, Will Deacon wrote:
> >>> Please just give me the time I asked for. If you want to help out in the
> >>> meantime, there are plenty of patches that need reviewing...
> >>
> >> It was a mistake on my part, and I sincerely apologize for wasting
> >> community review resources and disrupting your schedule.
> >>
> >> I will absolutely back off now and wait for your official series. Lesson
> >> learned. Thanks for your patience and for calling me out on this.
> > 
> > So I've mostly got the old series back on its feet:
> > 
> >   https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=cpu-hotplug
> 
> Hi Will,
> 
> I tested the above-mentioned latest patch on v7.2-rc1 with error inject
> on QEMU, which constructed the following errors:
> 
> 1、CPU4 does not support 52-bit VA
> 
> 2、CPU6 does not support 4K granule
> 
> 3、CPU16 and CPU17 call cpu_die_early() early in check_early_cpu_features().
> 
> 4、CPU18 call cpu_panic_kernel() early in check_early_cpu_features().
> 
> The error output is not correct especially for CPU4, CPU6, and CPU18 as
> below, it seems that some error messages are overlapping on the same
> CPU, and some errors are causing the CPU to be misidentified.:
> 
> (This leaves another blind spot where the 'failed to report alive state'
> message is skipped for CPU16 and CPU17, as pointed out in
> https://lore.kernel.org/all/bddf7a68-7789-4ec2-819c-aaaee8173c70@huawei.com/):
> 
> [    0.594323] CPU16: will not boot
> [    0.605818] CPU17: will not boot
> 
> ...
> 
> [   11.052387] CPU4 failed to report alive state
> [   11.059799] Parallel CPU bringup failed; consider passing
> "cpuhp.parallel=off" for a more accurate diagnosis.
> [   11.060179] CPU4 detected lack of support for 52-bit VAs
> [   11.060426] CPU4 detected lack of support for 4K granules
> 
> [   11.061103] Kernel panic - not syncing: CPU4 detected unsupported
> configuration
> [   11.061534] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted
> 7.2.0-rc1-00019-g52296829d92b #305 PREEMPT
> [   11.062052] Hardware name: linux,dummy-virt (DT)
> [   11.062230] Call trace:
> [   11.062339]  show_stack+0x18/0x24 (C)
> [   11.062528]  dump_stack_lvl+0x11c/0x168
> [   11.062684]  dump_stack+0x18/0x24
> [   11.062818]  vpanic+0x568/0x574
> [   11.062947]  do_panic_on_target_cpu+0x0/0x1c
> [   11.063111]  secondary_start_kernel+0x0/0x188
> [   11.063276]  cpuhp_bringup_ap+0x244/0x254
> [   11.063430]  cpuhp_invoke_callback+0x168/0x2ac
> [   11.063594]  __cpuhp_invoke_callback_range+0x90/0x118
> [   11.063776]  _cpu_up+0xec/0x1b8
> [   11.063905]  cpu_up+0xcc/0x158
> [   11.064032]  cpuhp_bringup_mask+0x9c/0xe0
> [   11.064189]  bringup_nonboot_cpus+0x12c/0x14c
> [   11.064352]  smp_init+0x30/0x8c
> [   11.064481]  kernel_init_freeable+0x18c/0x40c
> [   11.064645]  kernel_init+0x24/0x1dc
> [   11.064785]  ret_from_fork+0x10/0x20
> [   11.066612] SMP: stopping secondary CPUs
> [   11.068198] ---[ end Kernel panic - not syncing: CPU4 detected
> unsupported configuration ]---

I think this is actually working as intended. CPU4 has detected the
problems and the system has panicked as expected. Systems like this are
horribly broken anyway, so if you _really_ need to identify the CPUs
causing problems, you can disable parallel onlining on the cmdline (as
the diagnostic message above suggests).

Will