Re: [PATCH] arm64: smp: distinguish secondary CPUs that hang after reaching head.S

[Anshuman Khandual]

On 23/07/26 8:19 AM, Jinjie Ruan wrote:
> 
> 在 2026/7/22 19:30, Naman Jain 写道:
>> When a secondary CPU fails to come online, __cpu_up() falls back to
>> __early_cpu_boot_status, but boot status 0x0 is ambiguous: it cannot
>> distinguish a CPU that never executed head.S (firmware/hypervisor never
>> dispatched it, so it never ran a single instruction) from one that
>> entered head.S, started executing, and then got stuck somewhere in kernel
>> bring-up. Add a change to let us tell those two cases apart, which
>> narrows down where to look when a CPU goes missing during boot.
> I previously encountered this issue when debugging the parallel startup
> of ARM64 secondary cores. It is difficult for the kernel to determine
> whether the secondary core is hung in the firmware or whether it has not
> executed a single instruction. So I think this motive is reasonable.

Why should kernel determine the difference here ? Would not the firmware
know if it has started any secondary CPU for the kernel which must have
come inside head.S ? If the cpu gets hung inside firmware while starting
up then the debug responsibilities belong there instead.

Still wondering what's the rationale for this change.