[PATCH] x86/ACPI: ignore processors which cannot be brought online

[Jan Beulich <jbeulich@xxxxxxxx>]

ACPI 6.3 introduced a flag allowing to tell MADT entries describing
hotpluggable processors from ones which are simply placeholders (often
used by firmware writers to simplify handling there).

Inspired by a Linux patch by Mario Limonciello <mario.limonciello@xxxxxxx>.

Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/acpi/boot.c
+++ b/xen/arch/x86/acpi/boot.c
@@ -53,6 +53,8 @@ bool __initdata acpi_ioapic;
 static bool __initdata acpi_skip_timer_override;
 boolean_param("acpi_skip_timer_override", acpi_skip_timer_override);
 
+static uint8_t __initdata madt_revision;
+
 static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
 
 /* --------------------------------------------------------------------------
@@ -64,6 +66,8 @@ static int __init acpi_parse_madt(struct
        struct acpi_table_madt *madt =
                container_of(table, struct acpi_table_madt, header);
 
+       madt_revision = madt->header.revision;
+
        if (madt->address) {
                acpi_lapic_addr = (u64) madt->address;
 
@@ -86,6 +90,12 @@ acpi_parse_x2apic(struct acpi_subtable_h
        if (BAD_MADT_ENTRY(processor, end))
                return -EINVAL;
 
+       /* 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) {
                acpi_table_print_madt_entry(header);
@@ -136,6 +146,12 @@ acpi_parse_lapic(struct acpi_subtable_he
        if (BAD_MADT_ENTRY(processor, end))
                return -EINVAL;
 
+       /* 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)
                acpi_table_print_madt_entry(header);
--- a/xen/include/acpi/actbl1.h
+++ b/xen/include/acpi/actbl1.h
@@ -858,7 +858,8 @@ struct acpi_madt_generic_translator {
 
 /* MADT Local APIC flags */
 
-#define ACPI_MADT_ENABLED           (1)        /* 00: Processor is usable if 
set */
+#define ACPI_MADT_ENABLED           (1 << 0)   /* 00: Processor is usable if 
set */
+#define ACPI_MADT_ONLINE_CAPABLE    (1 << 1)   /* 01: Processor can be onlined 
*/
 
 /* MADT MPS INTI flags (inti_flags) */