Since KVM_MAX_VCPUS is currently defined to 1024 for x86 as shown in
arch/x86/include/asm/kvm_host.h, update QEMU limits to the same number.

In case KVM could not support the specified number of vcpus, QEMU would
return the following error message:

  qemu-system-x86_64: kvm_init_vcpu: kvm_get_vcpu failed (xxx): Invalid argument

Also, keep max_cpus at 288 for machine version 8.0 and older.

Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Julia Suvorova <jusual@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 hw/i386/pc_q35.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 6b9fd4d537..b26fd9bbaf 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -368,12 +368,12 @@ 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->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);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
-    m->max_cpus = 288;
 }
 
 static void pc_q35_8_1_machine_options(MachineClass *m)
@@ -396,6 +396,7 @@ static void pc_q35_8_0_machine_options(MachineClass *m)
 
     /* For pc-q35-8.0 and older, use SMBIOS 2.8 by default */
     pcmc->default_smbios_ep_type = SMBIOS_ENTRY_POINT_TYPE_32;
+    m->max_cpus = 288;
 }
 
 DEFINE_Q35_MACHINE(v8_0, "pc-q35-8.0", NULL,
-- 
2.34.1

On Wed, Jun 07, 2023 at 03:57:17PM -0500, Suravee Suthikulpanit wrote:
> Since KVM_MAX_VCPUS is currently defined to 1024 for x86 as shown in
> arch/x86/include/asm/kvm_host.h, update QEMU limits to the same number.
> 
> In case KVM could not support the specified number of vcpus, QEMU would
> return the following error message:
> 
>   qemu-system-x86_64: kvm_init_vcpu: kvm_get_vcpu failed (xxx): Invalid argument
> 
> Also, keep max_cpus at 288 for machine version 8.0 and older.
> 
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Julia Suvorova <jusual@redhat.com>
> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>  hw/i386/pc_q35.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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