[PATCH V1 3/4] hw/acpi: Reflect ACPI vCPU {present, enabled} states in ACPI _STA.{PRES, ENA} Bits

[Salil Mehta via <qemu-devel@nongnu.org>]

Reflect the ACPI CPU hotplug `is_{present, enabled}` states in the `_STA.PRES`
(presence) and `_STA.ENA` (enabled) bits when the guest kernel evaluates the
ACPI `_STA` method during initialization, as well as when vCPUs are hot-plugged
or hot-unplugged. The presence of unplugged vCPUs may need to be deliberately
*simulated* at the ACPI level to maintain a *persistent* view of vCPUs for the
guest kernel.

Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 hw/acpi/cpu.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
index 700aa855e9..23ea2b9c70 100644
--- a/hw/acpi/cpu.c
+++ b/hw/acpi/cpu.c
@@ -63,10 +63,11 @@ static uint64_t cpu_hotplug_rd(void *opaque, hwaddr addr, unsigned size)
     cdev = &cpu_st->devs[cpu_st->selector];
     switch (addr) {
     case ACPI_CPU_FLAGS_OFFSET_RW: /* pack and return is_* fields */
-        val |= cdev->cpu ? 1 : 0;
+        val |= cdev->is_enabled ? 1 : 0;
         val |= cdev->is_inserting ? 2 : 0;
         val |= cdev->is_removing  ? 4 : 0;
         val |= cdev->fw_remove  ? 16 : 0;
+        val |= cdev->is_present ? 32 : 0;
         trace_cpuhp_acpi_read_flags(cpu_st->selector, val);
         break;
     case ACPI_CPU_CMD_DATA_OFFSET_RW:
@@ -376,6 +377,7 @@ const VMStateDescription vmstate_cpu_hotplug = {
 #define CPU_REMOVE_EVENT  "CRMV"
 #define CPU_EJECT_EVENT   "CEJ0"
 #define CPU_FW_EJECT_EVENT "CEJF"
+#define CPU_PRESENT       "CPRS"
 
 void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
                     build_madt_cpu_fn build_madt_cpu, hwaddr base_addr,
@@ -436,7 +438,9 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
         aml_append(field, aml_named_field(CPU_EJECT_EVENT, 1));
         /* tell firmware to do device eject, write only */
         aml_append(field, aml_named_field(CPU_FW_EJECT_EVENT, 1));
-        aml_append(field, aml_reserved_field(3));
+        /* 1 if present, read only */
+        aml_append(field, aml_named_field(CPU_PRESENT, 1));
+        aml_append(field, aml_reserved_field(2));
         aml_append(field, aml_named_field(CPU_COMMAND, 8));
         aml_append(cpu_ctrl_dev, field);
 
@@ -466,6 +470,7 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
         Aml *ctrl_lock = aml_name("%s.%s", cphp_res_path, CPU_LOCK);
         Aml *cpu_selector = aml_name("%s.%s", cphp_res_path, CPU_SELECTOR);
         Aml *is_enabled = aml_name("%s.%s", cphp_res_path, CPU_ENABLED);
+        Aml *is_present = aml_name("%s.%s", cphp_res_path, CPU_PRESENT);
         Aml *cpu_cmd = aml_name("%s.%s", cphp_res_path, CPU_COMMAND);
         Aml *cpu_data = aml_name("%s.%s", cphp_res_path, CPU_DATA);
         Aml *ins_evt = aml_name("%s.%s", cphp_res_path, CPU_INSERT_EVENT);
@@ -494,13 +499,26 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
         {
             Aml *idx = aml_arg(0);
             Aml *sta = aml_local(0);
+            Aml *ifctx2;
+            Aml *else_ctx;
 
             aml_append(method, aml_acquire(ctrl_lock, 0xFFFF));
             aml_append(method, aml_store(idx, cpu_selector));
             aml_append(method, aml_store(zero, sta));
-            ifctx = aml_if(aml_equal(is_enabled, one));
+            ifctx = aml_if(aml_equal(is_present, one));
             {
-                aml_append(ifctx, aml_store(aml_int(0xF), sta));
+                ifctx2 = aml_if(aml_equal(is_enabled, one));
+                {
+                    /* cpu is present and enabled */
+                    aml_append(ifctx2, aml_store(aml_int(0xF), sta));
+                }
+                aml_append(ifctx, ifctx2);
+                else_ctx = aml_else();
+                {
+                    /* cpu is present but disabled */
+                    aml_append(else_ctx, aml_store(aml_int(0xD), sta));
+                }
+                aml_append(ifctx, else_ctx);
             }
             aml_append(method, ifctx);
             aml_append(method, aml_release(ctrl_lock));
-- 
2.34.1