Re: [PATCH for-4.22] x86/kexec: Check for a good per-cpu area before accessing IDTs

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 6/22/26 7:20 PM, Andrew Cooper wrote:
> Prior to commit 9c20d3c5915d ("x86/IDT: Make idt_tables[] be per_cpu(idt)"),
> the global idt_tables[] was always safe to use for CPUs in any state.
>
> However, not-yet-onlined CPUs (e.g. MADT with more entries than exist in
> practice) or offlined CPUs (e.g. xen-hptool) have their per-cpu pointer
> poisoned to detect incorrect uses.  machine_kexec() trips over the posion when
> clobbering #MC entry paths.
>
> This fixes a fatal #GP (non-canonical memory reference) when trying to enter
> the crash kernel.
>
> Fixes: 9c20d3c5915d ("x86/IDT: Make idt_tables[] be per_cpu(idt)")
> Reported-by: Lin Liu <Lin.Liu01@xxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Teddy Astie <teddy.astie@xxxxxxxxxx>
> CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> CC: Lin Liu <Lin.Liu01@xxxxxxxxxx>
>
> The fix here is a bit ugly.  nmi_shootdown_cpus() uses the cpu_online_map but
> this is wrong too; it misses parked CPUs, which do want to be captured.
>
> For 4.22.  This is the minimal fix to stop systems crashing, but more work is
> needed to make this path fully robust.
> ---
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

Thanks.

~ Oleksii