x86/ACPI: Ignore entries with invalid APIC IDs when parsing MADT

It seems some firmwares put dummy entries in the ACPI MADT table for non
existing processors. On my NUC11TNHi5 those have the invalid APIC ID
0xff. Linux already has code to handle those cases both in
acpi_parse_lapic [1] as well as in acpi_parse_x2apic [2]. So add the
same check to Xen.

Link: https://git.kernel.org/torvalds/c/f3bf1dbe64b62a2058dd1944c00990df203e8e7a # [1]
Link: https://git.kernel.org/torvalds/c/10daf10ab154e31237a8c07242be3063fb6a9bf4 # [2]
Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/acpi/boot.c

@@ -87,14 +87,17 @@ acpi_parse_x2apic(struct acpi_subtable_header *header, const unsigned long end)
 	if (BAD_MADT_ENTRY(processor, end))
 		return -EINVAL;
 
+	/* Ignore entries with invalid x2APIC ID */
+	if (processor->local_apic_id == 0xffffffff)
+		return 0;
+
 	/* Don't register processors that cannot be onlined. */
 	if (madt_revision >= 5 &&
 	    !(processor->lapic_flags & ACPI_MADT_ENABLED) &&
 	    !(processor->lapic_flags & ACPI_MADT_ONLINE_CAPABLE))
 		return 0;
 
-	if ((processor->lapic_flags & ACPI_MADT_ENABLED) ||
-	    processor->local_apic_id != 0xffffffff || opt_cpu_info) {
+	if ((processor->lapic_flags & ACPI_MADT_ENABLED) || opt_cpu_info) {
 		acpi_table_print_madt_entry(header);
 		log = true;
 	}
@@ -143,14 +146,17 @@ acpi_parse_lapic(struct acpi_subtable_header * header, const unsigned long end)
 	if (BAD_MADT_ENTRY(processor, end))
 		return -EINVAL;
 
+	/* Ignore entries with invalid APIC ID */
+	if (processor->id == 0xff)
+		return 0;
+
 	/* Don't register processors that cannot be onlined. */
 	if (madt_revision >= 5 &&
 	    !(processor->lapic_flags & ACPI_MADT_ENABLED) &&
 	    !(processor->lapic_flags & ACPI_MADT_ONLINE_CAPABLE))
 		return 0;
 
-	if ((processor->lapic_flags & ACPI_MADT_ENABLED) ||
-	    processor->id != 0xff || opt_cpu_info)
+	if ((processor->lapic_flags & ACPI_MADT_ENABLED) || opt_cpu_info)
 		acpi_table_print_madt_entry(header);
 
 	/* Record local apic id only when enabled */