[PATCH RFC V3 20/29] hw/arm, gicv3: Changes to update GIC with vCPU hot-plug notification

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

Virtual CPU hot-(un)plug events MUST be notified to the GIC. Introduce a
notfication mechanism to update any such events to GIC so that it can update its
vCPU to GIC CPU interface association.

This is required to implement a workaround to the limitations posed by the ARM
architecture. For details about the constraints and workarounds please check
below slides:

Link: https://kvm-forum.qemu.org/2023/talk/9SMPDQ/

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.c                      | 27 +++++++++++++--
 hw/intc/arm_gicv3_common.c         | 54 +++++++++++++++++++++++++++++-
 hw/intc/arm_gicv3_cpuif_common.c   |  5 +++
 hw/intc/gicv3_internal.h           |  1 +
 include/hw/arm/virt.h              |  1 +
 include/hw/intc/arm_gicv3_common.h | 22 ++++++++++++
 6 files changed, 107 insertions(+), 3 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 1556c362f7..9f7e07bd8e 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -685,6 +685,16 @@ static inline DeviceState *create_acpi_ged(VirtMachineState *vms)
     return dev;
 }
 
+static void virt_add_gic_cpuhp_notifier(VirtMachineState *vms)
+{
+    MachineClass *mc = MACHINE_GET_CLASS(vms);
+
+    if (mc->has_hotpluggable_cpus) {
+        Notifier *cpuhp_notifier = gicv3_cpuhp_notifier(vms->gic);
+        notifier_list_add(&vms->cpuhp_notifiers, cpuhp_notifier);
+    }
+}
+
 static void create_its(VirtMachineState *vms)
 {
     const char *itsclass = its_class_name();
@@ -960,6 +970,9 @@ static void create_gic(VirtMachineState *vms, MemoryRegion *mem)
     } else if (vms->gic_version == VIRT_GIC_VERSION_2) {
         create_v2m(vms);
     }
+
+    /* add GIC CPU hot(un)plug update notifier */
+    virt_add_gic_cpuhp_notifier(vms);
 }
 
 static void create_uart(const VirtMachineState *vms, int uart,
@@ -2472,6 +2485,8 @@ static void machvirt_init(MachineState *machine)
 
     create_fdt(vms);
 
+    notifier_list_init(&vms->cpuhp_notifiers);
+
     assert(possible_cpus->len == max_cpus);
     for (n = 0; n < possible_cpus->len; n++) {
         CPUArchId *cpu_slot;
@@ -3054,6 +3069,14 @@ static void virt_memory_plug(HotplugHandler *hotplug_dev,
                          dev, &error_abort);
 }
 
+static void virt_update_gic(VirtMachineState *vms, CPUState *cs)
+{
+    GICv3CPUHotplugInfo gic_info = { .gic = vms->gic, .cpu = cs };
+
+    /* notify gic to stitch GICC to this new cpu */
+    notifier_list_notify(&vms->cpuhp_notifiers, &gic_info);
+}
+
 static void virt_cpu_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                               Error **errp)
 {
@@ -3128,7 +3151,7 @@ static void virt_cpu_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
      * vCPUs have their GIC state initialized during machvit_init().
      */
     if (vms->acpi_dev) {
-        /* TODO: update GIC about this hotplug change here */
+        virt_update_gic(vms, cs);
         wire_gic_cpu_irqs(vms, cs);
     }
 
@@ -3214,7 +3237,7 @@ static void virt_cpu_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
     /* TODO: update the acpi cpu hotplug state for cpu hot-unplug */
 
     unwire_gic_cpu_irqs(vms, cs);
-    /* TODO: update the GIC about this hot unplug change */
+    virt_update_gic(vms, cs);
 
     /* TODO: unregister cpu for reset & update F/W info for the next boot */
 
diff --git a/hw/intc/arm_gicv3_common.c b/hw/intc/arm_gicv3_common.c
index 183d2de7eb..155342055b 100644
--- a/hw/intc/arm_gicv3_common.c
+++ b/hw/intc/arm_gicv3_common.c
@@ -33,7 +33,6 @@
 #include "hw/arm/linux-boot-if.h"
 #include "sysemu/kvm.h"
 
-
 static void gicv3_gicd_no_migration_shift_bug_post_load(GICv3State *cs)
 {
     if (cs->gicd_no_migration_shift_bug) {
@@ -366,6 +365,56 @@ void gicv3_init_irqs_and_mmio(GICv3State *s, qemu_irq_handler handler,
     }
 }
 
+static int arm_gicv3_get_proc_num(GICv3State *s, CPUState *cpu)
+{
+    uint64_t mp_affinity;
+    uint64_t gicr_typer;
+    uint64_t cpu_affid;
+    int i;
+
+    mp_affinity = object_property_get_uint(OBJECT(cpu), "mp-affinity", NULL);
+    /* match the cpu mp-affinity to get the gic cpuif number */
+    for (i = 0; i < s->num_cpu; i++) {
+        gicr_typer = s->cpu[i].gicr_typer;
+        cpu_affid = (gicr_typer >> 32) & 0xFFFFFF;
+        if (cpu_affid == mp_affinity) {
+            return i;
+        }
+    }
+
+    return -1;
+}
+
+static void arm_gicv3_cpu_update_notifier(Notifier *notifier, void * data)
+{
+    GICv3CPUHotplugInfo *gic_info = (GICv3CPUHotplugInfo *)data;
+    CPUState *cpu = gic_info->cpu;
+    int gic_cpuif_num;
+    GICv3State *s;
+
+    s = ARM_GICV3_COMMON(gic_info->gic);
+
+    /* this shall get us mapped gicv3 cpuif corresponding to mpidr */
+    gic_cpuif_num = arm_gicv3_get_proc_num(s, cpu);
+    if (gic_cpuif_num < 0) {
+        error_report("Failed to associate cpu %d with any GIC cpuif",
+                     cpu->cpu_index);
+        abort();
+    }
+
+    /* check if update is for vcpu hot-unplug */
+    if (qemu_enabled_cpu(cpu)) {
+        s->cpu[gic_cpuif_num].cpu = NULL;
+        return;
+    }
+
+    /* re-stitch the gic cpuif to this new cpu */
+    gicv3_set_gicv3state(cpu, &s->cpu[gic_cpuif_num]);
+    gicv3_set_cpustate(&s->cpu[gic_cpuif_num], cpu);
+
+    /* TODO: initialize the registers info for this newly added cpu */
+}
+
 static void arm_gicv3_common_realize(DeviceState *dev, Error **errp)
 {
     GICv3State *s = ARM_GICV3_COMMON(dev);
@@ -488,6 +537,8 @@ static void arm_gicv3_common_realize(DeviceState *dev, Error **errp)
         s->cpu[cpuidx - 1].gicr_typer |= GICR_TYPER_LAST;
     }
 
+    s->cpu_update_notifier.notify = arm_gicv3_cpu_update_notifier;
+
     s->itslist = g_ptr_array_new();
 }
 
@@ -495,6 +546,7 @@ static void arm_gicv3_finalize(Object *obj)
 {
     GICv3State *s = ARM_GICV3_COMMON(obj);
 
+    notifier_remove(&s->cpu_update_notifier);
     g_free(s->redist_region_count);
 }
 
diff --git a/hw/intc/arm_gicv3_cpuif_common.c b/hw/intc/arm_gicv3_cpuif_common.c
index ff1239f65d..381cf2754b 100644
--- a/hw/intc/arm_gicv3_cpuif_common.c
+++ b/hw/intc/arm_gicv3_cpuif_common.c
@@ -20,3 +20,8 @@ void gicv3_set_gicv3state(CPUState *cpu, GICv3CPUState *s)
 
     env->gicv3state = (void *)s;
 };
+
+void gicv3_set_cpustate(GICv3CPUState *s, CPUState *cpu)
+{
+    s->cpu = cpu;
+}
diff --git a/hw/intc/gicv3_internal.h b/hw/intc/gicv3_internal.h
index bc9f518fe8..42441c19c6 100644
--- a/hw/intc/gicv3_internal.h
+++ b/hw/intc/gicv3_internal.h
@@ -861,5 +861,6 @@ static inline void gicv3_cache_all_target_cpustates(GICv3State *s)
 }
 
 void gicv3_set_gicv3state(CPUState *cpu, GICv3CPUState *s);
+void gicv3_set_cpustate(GICv3CPUState *s, CPUState *cpu);
 
 #endif /* QEMU_ARM_GICV3_INTERNAL_H */
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index d711cab46d..9c728ba042 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -181,6 +181,7 @@ struct VirtMachineState {
     char *oem_id;
     char *oem_table_id;
     bool ns_el2_virt_timer_irq;
+    NotifierList cpuhp_notifiers;
 };
 
 #define VIRT_ECAM_ID(high) (high ? VIRT_HIGH_PCIE_ECAM : VIRT_PCIE_ECAM)
diff --git a/include/hw/intc/arm_gicv3_common.h b/include/hw/intc/arm_gicv3_common.h
index cd09bee3bc..496b198016 100644
--- a/include/hw/intc/arm_gicv3_common.h
+++ b/include/hw/intc/arm_gicv3_common.h
@@ -293,6 +293,7 @@ struct GICv3State {
     GICv3CPUState *gicd_irouter_target[GICV3_MAXIRQ];
     uint32_t gicd_nsacr[DIV_ROUND_UP(GICV3_MAXIRQ, 16)];
 
+    Notifier cpu_update_notifier;
     GICv3CPUState *cpu;
     /* List of all ITSes connected to this GIC */
     GPtrArray *itslist;
@@ -342,6 +343,27 @@ struct ARMGICv3CommonClass {
 
 void gicv3_init_irqs_and_mmio(GICv3State *s, qemu_irq_handler handler,
                               const MemoryRegionOps *ops);
+/**
+ * Structure used by GICv3 CPU hotplug notifier
+ */
+typedef struct GICv3CPUHotplugInfo {
+    DeviceState *gic; /* GICv3State */
+    CPUState *cpu;
+} GICv3CPUHotplugInfo;
+
+/**
+ * gicv3_cpuhp_notifier
+ *
+ * Returns CPU hotplug notifier which could be used to update GIC about any
+ * CPU hot(un)plug events.
+ *
+ * Returns: Notifier initialized with CPU Hot(un)plug update function
+ */
+static inline Notifier *gicv3_cpuhp_notifier(DeviceState *dev)
+{
+    GICv3State *s = ARM_GICV3_COMMON(dev);
+    return &s->cpu_update_notifier;
+}
 
 /**
  * gicv3_class_name
-- 
2.34.1