[PATCH] pc: q35: Bump max_cpus to 4096

[Ani Sinha <anisinha@redhat.com>]

Since commit f10a570b093e6 ("KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS to allow up to 4096 vCPUs")
Linux kernel can support upto a maximum number of 4096 vCPUS when MAXSMP is
enabled in the kernel. So bump up the max_cpus value for q35 machines versions
8.3 and newer to 4096. Older q35 machines versions 8.2 and older continue to
support 1024 maximum vcpus as before.

If KVM is not able to support the specified number of vcpus, QEMU would
return the following error messages:

$ ./qemu-system-x86_64 -cpu host -accel kvm -machine q35 -smp 4096
qemu-system-x86_64: -accel kvm: warning: Number of SMP cpus requested (4096) exceeds the recommended cpus supported by KVM (12)
Number of SMP cpus requested (4096) exceeds the maximum cpus supported by KVM (1024)

Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Julia Suvorova <jusual@redhat.com>
Signed-off-by: Ani Sinha <anisinha@redhat.com>
---
 hw/i386/pc_q35.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 4f3e5412f6..2ed57814e1 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -375,7 +375,7 @@ static void pc_q35_machine_options(MachineClass *m)
     m->default_nic = "e1000e";
     m->default_kernel_irqchip_split = false;
     m->no_floppy = 1;
-    m->max_cpus = 1024;
+    m->max_cpus = 4096;
     m->no_parallel = !module_object_class_by_name(TYPE_ISA_PARALLEL);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_AMD_IOMMU_DEVICE);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE);
@@ -383,12 +383,22 @@ static void pc_q35_machine_options(MachineClass *m)
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
 }
 
-static void pc_q35_8_2_machine_options(MachineClass *m)
+static void pc_q35_8_3_machine_options(MachineClass *m)
 {
     pc_q35_machine_options(m);
     m->alias = "q35";
 }
 
+DEFINE_Q35_MACHINE(v8_3, "pc-q35-8.3", NULL,
+                   pc_q35_8_3_machine_options);
+
+static void pc_q35_8_2_machine_options(MachineClass *m)
+{
+    pc_q35_8_3_machine_options(m);
+    m->alias = NULL;
+    m->max_cpus = 1024;
+}
+
 DEFINE_Q35_MACHINE(v8_2, "pc-q35-8.2", NULL,
                    pc_q35_8_2_machine_options);
 
@@ -396,7 +406,6 @@ static void pc_q35_8_1_machine_options(MachineClass *m)
 {
     PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
     pc_q35_8_2_machine_options(m);
-    m->alias = NULL;
     pcmc->broken_32bit_mem_addr_check = true;
     compat_props_add(m->compat_props, hw_compat_8_1, hw_compat_8_1_len);
     compat_props_add(m->compat_props, pc_compat_8_1, pc_compat_8_1_len);
-- 
2.42.0