Re: [PATCH v5 02/22] cc_platform: Add new attribute to prevent ACPI CPU hotplug

[Dave Hansen]

On 7/13/22 04:09, Kai Huang wrote:
...
> "TDX doesn’t support adding or removing CPUs from TDX security perimeter. The
> BIOS should prevent CPUs from being hot-added or hot-removed after platform
> boots."

That's a start.  It also probably needs to say that the security
perimeter includes all logical CPUs, though.

>  static int acpi_map_cpu2node(acpi_handle handle, int cpu, int physid)
>  {
> @@ -819,6 +820,12 @@ int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid,
> u32 acpi_id,
>  {
>         int cpu;
>  
> +       if (platform_tdx_enabled()) {
> +               pr_err("BIOS bug: CPU (physid %u) hot-added on TDX enabled
> platform. Reject it.\n",
> +                               physid);
> +               return -EINVAL;
> +       }

Is this the right place?  There are other sanity checks in
acpi_processor_hotadd_init() and it seems like a better spot.

>         cpu = acpi_register_lapic(physid, acpi_id, ACPI_MADT_ENABLED);
>         if (cpu < 0) {
>                 pr_info("Unable to map lapic to logical cpu number\n");
> @@ -835,6 +842,10 @@ EXPORT_SYMBOL(acpi_map_cpu);
>  
>  int acpi_unmap_cpu(int cpu)
>  {
> +       if (platform_tdx_enabled())
> +               pr_err("BIOS bug: CPU %d hot-removed on TDX enabled platform.
> TDX is broken. Please reboot the machine.\n",
> +                               cpu);
> +
>  #ifdef CONFIG_ACPI_NUMA
>         set_apicid_to_node(per_cpu(x86_cpu_to_apicid, cpu), NUMA_NO_NODE);
>  #endif