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

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