When QEMU builds the MADT table, modifications are needed to include information
about possible vCPUs that are exposed as ACPI-disabled (i.e., `_STA.Enabled=0`).
This new information will help the guest kernel pre-size its resources during
boot time. Pre-sizing based on possible vCPUs will facilitate the future
hot-plugging of the currently disabled vCPUs.

Additionally, this change addresses updates to the ACPI MADT GIC CPU interface
flags, as introduced in the UEFI ACPI 6.5 specification. These updates enable
deferred virtual CPU onlining in the guest kernel.

Link: https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#gic-cpu-interface-gicc-structure

Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 hw/arm/virt-acpi-build.c | 36 ++++++++++++++++++++++++++++++------
 include/hw/acpi/cpu.h    | 18 ++++++++++++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 32238170ab..ff104b3496 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -663,6 +663,29 @@ static void build_append_gicr(GArray *table_data, uint64_t base, uint32_t size)
     build_append_int_noprefix(table_data, size, 4); /* Discovery Range Length */
 }
 
+static uint32_t virt_acpi_get_gicc_flags(CPUState *cpu)
+{
+    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
+
+    /* can only exist in 'enabled' state */
+    if (!mc->has_hotpluggable_cpus) {
+        return 1;
+    }
+
+    /*
+     * ARM GIC CPU Interface can be 'online-capable' or 'enabled' at boot
+     * We MUST set 'online-capable' bit for all hotpluggable CPUs except the
+     * first/boot CPU. Cold-booted CPUs without 'Id' can also be unplugged.
+     * Though as-of-now this is only used as a debugging feature.
+     *
+     *   UEFI ACPI Specification 6.5
+     *   Section: 5.2.12.14. GIC CPU Interface (GICC) Structure
+     *   Table:   5.37 GICC CPU Interface Flags
+     *   Link: https://uefi.org/specs/ACPI/6.5
+     */
+    return cpu && !cpu->cpu_index ? 1 : (1 << 3);
+}
+
 static void
 build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
 {
@@ -689,12 +712,13 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
     build_append_int_noprefix(table_data, vms->gic_version, 1);
     build_append_int_noprefix(table_data, 0, 3);   /* Reserved */
 
-    for (i = 0; i < MACHINE(vms)->smp.cpus; i++) {
-        ARMCPU *armcpu = ARM_CPU(qemu_get_cpu(i));
+    for (i = 0; i < MACHINE(vms)->smp.max_cpus; i++) {
+        CPUState *cpu = qemu_get_possible_cpu(i);
         uint64_t physical_base_address = 0, gich = 0, gicv = 0;
         uint32_t vgic_interrupt = vms->virt ? ARCH_GIC_MAINT_IRQ : 0;
-        uint32_t pmu_interrupt = arm_feature(&armcpu->env, ARM_FEATURE_PMU) ?
-                                             VIRTUAL_PMU_IRQ : 0;
+        uint32_t pmu_interrupt = vms->pmu ? VIRTUAL_PMU_IRQ : 0;
+        uint32_t flags = virt_acpi_get_gicc_flags(cpu);
+        uint64_t mpidr = acpi_get_cpu_archid(i);
 
         if (vms->gic_version == VIRT_GIC_VERSION_2) {
             physical_base_address = memmap[VIRT_GIC_CPU].base;
@@ -709,7 +733,7 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
         build_append_int_noprefix(table_data, i, 4);    /* GIC ID */
         build_append_int_noprefix(table_data, i, 4);    /* ACPI Processor UID */
         /* Flags */
-        build_append_int_noprefix(table_data, 1, 4);    /* Enabled */
+        build_append_int_noprefix(table_data, flags, 4);
         /* Parking Protocol Version */
         build_append_int_noprefix(table_data, 0, 4);
         /* Performance Interrupt GSIV */
@@ -723,7 +747,7 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
         build_append_int_noprefix(table_data, vgic_interrupt, 4);
         build_append_int_noprefix(table_data, 0, 8);    /* GICR Base Address*/
         /* MPIDR */
-        build_append_int_noprefix(table_data, arm_cpu_mp_affinity(armcpu), 8);
+        build_append_int_noprefix(table_data, mpidr, 8);
         /* Processor Power Efficiency Class */
         build_append_int_noprefix(table_data, 0, 1);
         /* Reserved */
diff --git a/include/hw/acpi/cpu.h b/include/hw/acpi/cpu.h
index 32654dc274..4d6ae5453f 100644
--- a/include/hw/acpi/cpu.h
+++ b/include/hw/acpi/cpu.h
@@ -75,4 +75,22 @@ extern const VMStateDescription vmstate_cpu_hotplug;
     VMSTATE_STRUCT(cpuhp, state, 1, \
                    vmstate_cpu_hotplug, CPUHotplugState)
 
+/**
+ * acpi_get_cpu_archid:
+ * @cpu_index: possible vCPU for which arch-id needs to be retreived
+ *
+ * Fetches the vCPU arch-id of the possible vCPU. This should be same
+ * same as the one configured at KVM Host.
+ *
+ * Returns: arch-id of the possible vCPU
+ */
+static inline uint64_t acpi_get_cpu_archid(int cpu_index)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    const CPUArchIdList *possible_cpus = ms->possible_cpus;
+
+    assert((cpu_index >= 0) && (cpu_index < possible_cpus->len));
+
+    return possible_cpus->cpus[cpu_index].arch_id;
+}
 #endif
-- 
2.34.1