[Qemu-devel] [PATCH] pc: q35: bump max_cpus to INT32_MAX

[Radim Krčmář]

QEMU does not allocate based on machine's max_cpus, but only uses it to
limit the maximum selected by user and the actual limit of VCPUs is
enfoced by other components:
 - machine without vIOMMU ends at 255 VCPUs
 - TCG currently doesn't support x2APIC, so it also ends below 256
 - KVM with vIOMMU cannot exceed the KVM limit (currently 288)

Using a big value should bring no drawbacks and the benefit is that
components (especially out-of-tree KVM) can bump their limits without
touching machine's max_cpus.

max_cpus is unsigned, but it is treated as signed at least in printf and
the other two billion VCPU won't be needed for a while, so we can ignore
possible bugs by using signed max.

Signed-off-by: Radim Krčmář <address@hidden>
---
  Should the 2.9 machine type still have 288?
---
 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 dd792a8547b3..3d5710ca20e0 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -298,7 +298,7 @@ static void pc_q35_machine_options(MachineClass *m)
     m->default_display = "std";
     m->no_floppy = 1;
     m->has_dynamic_sysbus = true;
-    m->max_cpus = 288;
+    m->max_cpus = INT32_MAX;
 }
 
 static void pc_q35_2_9_machine_options(MachineClass *m)
@@ -314,6 +314,7 @@ static void pc_q35_2_8_machine_options(MachineClass *m)
 {
     pc_q35_2_9_machine_options(m);
     m->alias = NULL;
+    m->max_cpus = 288;
     SET_MACHINE_COMPAT(m, PC_COMPAT_2_8);
 }
 
-- 
2.12.0