From: Salil Mehta <salil.me...@huawei.com>
To support a vCPU hot-add–like model on ARM, the virt machine may be setup with
more CPUs than are active at boot. These additional CPUs are fully realized in
KVM and listed in ACPI tables from the start, but begin in a disabled state.
They can later be brought online or taken offline under host or platform policy
control. The CPU topology is fixed at VM creation time and cannot change
dynamically on ARM. Therefore, we must determine precisely the 'maxcpus' value
that applies for the full lifetime of the VM.
On ARM, this deferred online-capable model is only valid if:
- The GIC version is 3 or higher, and
- Each non-boot CPU’s GIC CPU Interface is marked “online-capable” in its
ACPI GICC structure (UEFI ACPI Specification 6.5, §5.2.12.14, Table 5.37
“GICC CPU Interface Flags”), and
- The chosen accelerator supports safe deferred CPU online:
* TCG with multi-threaded TCG (MTTCG) enabled
* KVM (on supported hosts)
* Not HVF or QTest
This patch sizes the machine’s max-possible CPUs during VM init:
- If all conditions are satisfied, retain the full set of CPUs corresponding
to (`-smp cpus` + `-smp disabledcpus`), allowing the additional (initially
disabled) CPUs to participate in later policy-driven online.
- Otherwise, clamp the max-possible CPUs to the boot-enabled count
(`-smp disabledcpus=0` equivalent) to avoid advertising CPUs the guest can
never use.
A new MachineClass flag, `has_online_capable_cpus`, records whether the machine
supports deferred vCPU online. This is usable by other machine types as well.
Signed-off-by: Salil Mehta <salil.me...@huawei.com>
---
hw/arm/virt.c | 84 ++++++++++++++++++++++++++++++---------------
include/hw/boards.h | 1 +
2 files changed, 57 insertions(+), 28 deletions(-)
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index ef6be3660f..76f21bd56a 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2168,8 +2168,7 @@ static void machvirt_init(MachineState *machine)
bool has_ged = !vmc->no_ged;
unsigned int smp_cpus = machine->smp.cpus;
unsigned int max_cpus = machine->smp.max_cpus;
-
- possible_cpus = mc->possible_cpu_arch_ids(machine);
+ DeviceClass *dc;
/*
* In accelerated mode, the memory map is computed earlier in kvm_type()
@@ -2186,7 +2185,7 @@ static void machvirt_init(MachineState *machine)
* we are about to deal with. Once this is done, get rid of
* the object.
*/
- cpuobj = object_new(possible_cpus->cpus[0].type);
+ cpuobj = object_new(machine->cpu_type);
armcpu = ARM_CPU(cpuobj);
pa_bits = arm_pamax(armcpu);
@@ -2201,6 +2200,57 @@ static void machvirt_init(MachineState *machine)
*/
finalize_gic_version(vms);
+ /*
+ * The maximum number of CPUs depends on the GIC version, or on how
+ * many redistributors we can fit into the memory map (which in turn
+ * depends on whether this is a GICv3 or v4).
+ */
+ if (vms->gic_version == VIRT_GIC_VERSION_2) {
+ virt_max_cpus = GIC_NCPU;
+ } else {
+ virt_max_cpus = virt_redist_capacity(vms, VIRT_GIC_REDIST);
+ if (vms->highmem_redists) {
+ virt_max_cpus += virt_redist_capacity(vms, VIRT_HIGH_GIC_REDIST2);
+ }
+ }
+
+ if ((tcg_enabled() && !qemu_tcg_mttcg_enabled()) || hvf_enabled() ||
+ qtest_enabled() || vms->gic_version == VIRT_GIC_VERSION_2) {
+ max_cpus = machine->smp.max_cpus = smp_cpus;
+ if (mc->has_online_capable_cpus) {
+ if (vms->gic_version == VIRT_GIC_VERSION_2) {
+ warn_report("GICv2 does not support online-capable CPUs");
+ }
+ mc->has_online_capable_cpus = false;
+ }
+ }
+
+ if (mc->has_online_capable_cpus) {
+ max_cpus = smp_cpus + machine->smp.disabledcpus;
+ machine->smp.max_cpus = max_cpus;
+ }
+
+ if (max_cpus > virt_max_cpus) {
+ error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
+ "supported by machine 'mach-virt' (%d)",
+ max_cpus, virt_max_cpus);
+ if (vms->gic_version != VIRT_GIC_VERSION_2 && !vms->highmem_redists) {
+ error_printf("Try 'highmem-redists=on' for more CPUs\n");
+ }
+
+ exit(1);
+ }
+
+ dc = DEVICE_CLASS(object_class_by_name(machine->cpu_type));
+ if (!dc) {
+ error_report("CPU type '%s' not registered", machine->cpu_type);
+ exit(1);
+ }
+ dc->admin_power_state_supported = mc->has_online_capable_cpus;
+
+ /* uses smp.max_cpus to initialize all possible vCPUs */
+ possible_cpus = mc->possible_cpu_arch_ids(machine);
+
if (vms->secure) {
/*
* The Secure view of the world is the same as the NonSecure,
@@ -2235,31 +2285,6 @@ static void machvirt_init(MachineState *machine)
vms->psci_conduit = QEMU_PSCI_CONDUIT_HVC;
}
- /*
- * The maximum number of CPUs depends on the GIC version, or on how
- * many redistributors we can fit into the memory map (which in turn
- * depends on whether this is a GICv3 or v4).
- */
- if (vms->gic_version == VIRT_GIC_VERSION_2) {
- virt_max_cpus = GIC_NCPU;
- } else {
- virt_max_cpus = virt_redist_capacity(vms, VIRT_GIC_REDIST);
- if (vms->highmem_redists) {
- virt_max_cpus += virt_redist_capacity(vms, VIRT_HIGH_GIC_REDIST2);
- }
- }
-
- if (max_cpus > virt_max_cpus) {
- error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
- "supported by machine 'mach-virt' (%d)",
- max_cpus, virt_max_cpus);
- if (vms->gic_version != VIRT_GIC_VERSION_2 && !vms->highmem_redists) {
- error_printf("Try 'highmem-redists=on' for more CPUs\n");
- }
-
- exit(1);
- }
-
if (vms->secure && !tcg_enabled() && !qtest_enabled()) {
error_report("mach-virt: %s does not support providing "
"Security extensions (TrustZone) to the guest CPU",
@@ -3245,6 +3270,9 @@ static void virt_machine_class_init(ObjectClass *oc,
const void *data)
hc->plug = virt_machine_device_plug_cb;
hc->unplug_request = virt_machine_device_unplug_request_cb;
hc->unplug = virt_machine_device_unplug_cb;
+
+ mc->has_online_capable_cpus = true;
+
mc->nvdimm_supported = true;
mc->smp_props.clusters_supported = true;
mc->auto_enable_numa_with_memhp = true;
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 2b182d7817..b27c2326a2 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -302,6 +302,7 @@ struct MachineClass {
bool rom_file_has_mr;
int minimum_page_bits;
bool has_hotpluggable_cpus;
+ bool has_online_capable_cpus;
bool ignore_memory_transaction_failures;
int numa_mem_align_shift;
const char * const *valid_cpu_types;
--
2.34.1
