Virtual CPU hot-(un)plug events must be communicated to the GIC. Introduce a
notification mechanism to ensure these events are properly relayed to the GIC,
allowing it to update the accessibility of the GIC CPU interface and adjust the
vCPU-to-GIC CPU interface association accordingly.
This approach deviates from the standard ARM CPU architecture specification,
where the CPU-to-GIC interface is typically fixed and the accessibility of the
GIC CPU interface cannot be disabled. However, this workaround is necessary
to address limitations imposed by the ARM CPU architecture [1][2].
For more details regarding these constraints and the workarounds, please refer
to the slides below:
References:
[1] KVMForum 2023 Presentation: Challenges Revisited in Supporting Virt CPU
Hotplug on
architectures that don’t Support CPU Hotplug (like ARM64)
Link:
https://kvm-forum.qemu.org/2023/Challenges_Revisited_in_Supporting_Virt_CPU_Hotplug_-__ii0iNb3.pdf
(Slides 13,17,18)
[2] KVMForum 2020 Presentation: Challenges in Supporting Virtual CPU Hotplug on
SoC Based Systems (like ARM64)
Link: https://kvmforum2020.sched.com/event/eE4m
Co-developed-by: Keqian Zhu <zhukeqi...@huawei.com>
Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com>
Signed-off-by: Salil Mehta <salil.me...@huawei.com>
---
hw/arm/virt.c | 31 ++++++++++++++-
hw/intc/arm_gicv3_common.c | 60 +++++++++++++++++++++++++++++-
include/hw/arm/virt.h | 1 +
include/hw/intc/arm_gicv3_common.h | 23 ++++++++++++
4 files changed, 112 insertions(+), 3 deletions(-)
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 0a912919ec..295012bce1 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -703,6 +703,16 @@ 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();
@@ -979,6 +989,9 @@ 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,
@@ -2450,6 +2463,8 @@ 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;
@@ -3066,6 +3081,18 @@ static void virt_memory_plug(HotplugHandler *hotplug_dev,
dev, &error_abort);
}
+static void virt_update_gic(VirtMachineState *vms, CPUState *cs, bool plugging)
+{
+ GICv3CPUHotplugInfo gic_info = {
+ .gic = vms->gic,
+ .cpu = cs,
+ .cpu_plugging = plugging
+ };
+
+ /* 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)
{
@@ -3142,7 +3169,7 @@ static void virt_cpu_pre_plug(HotplugHandler
*hotplug_dev, DeviceState *dev,
* `machvirt_init()`.
*/
if (vms->acpi_dev) {
- /* TODO: update GIC about this hotplug change here */
+ virt_update_gic(vms, cs, true);
wire_gic_cpu_irqs(vms, cs);
}
}
@@ -3227,7 +3254,7 @@ 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, false);
/* 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 218ced1d9f..c21fff4903 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 +365,62 @@ 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;
+ ARMGICv3CommonClass *agcc;
+ int gic_cpuif_num;
+ GICv3State *s;
+
+ s = ARM_GICV3_COMMON(gic_info->gic);
+ agcc = ARM_GICV3_COMMON_GET_CLASS(s);
+
+ /* this shall get us mapped GICv3 CPU interface 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();
+ }
+
+ /* Update the GICv3 CPU interface accessibiltiy accordingly */
+ gicv3_set_cpustate(&s->cpu[gic_cpuif_num], cpu, gic_info->cpu_plugging);
+
+ if (!gic_info->cpu_plugging) {
+ return;
+ }
+
+ /* re-stitch the GICv3 CPU interface to this new vCPU */
+ gicv3_set_gicv3state(cpu, &s->cpu[gic_cpuif_num]);
+
+ /*
+ * define and register the GICv3 CPU interface `system registers` for
+ * this new vCPU being hotplugged
+ */
+ agcc->init_cpu_reginfo(cpu);
+}
+
static void arm_gicv3_common_realize(DeviceState *dev, Error **errp)
{
GICv3State *s = ARM_GICV3_COMMON(dev);
@@ -492,6 +547,8 @@ 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();
}
@@ -499,6 +556,7 @@ 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/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 98ce68eae1..0202f0252c 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -186,6 +186,7 @@ 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 3f585162f3..c02a810da9 100644
--- a/include/hw/intc/arm_gicv3_common.h
+++ b/include/hw/intc/arm_gicv3_common.h
@@ -295,6 +295,7 @@ 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;
@@ -345,6 +346,28 @@ 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;
+ bool cpu_plugging; /* CPU being plugged or unplugged */
+} 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
