[PATCH v4 6/6] hw/arm/virt: kvm: allow gicv3 by default if v2 cannot work

[Eric Auger]

At the moment if the end-user does not specify the gic-version along
with KVM acceleration, v2 is set by default. However most of the
systems now have GICv3 and sometimes they do not support GICv2
compatibility.

This patch keeps the default v2 selection in all cases except
in the KVM accelerated mode when either
- the host does not support GICv2 in-kernel emulation or
- number of VCPUS exceeds 8.

Those cases did not work anyway so we do not break any compatibility.
Now we get v3 selected in such a case.

Signed-off-by: Eric Auger <address@hidden>
Reported-by: Dr. David Alan Gilbert <address@hidden>

---

v3 -> v4:
- Deal with the case where v3 is not supported by the host and
  the number of vcpus exceeds 8

v2 -> v3:
- add ()
---
 hw/arm/virt.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index f5ff2d9006..6becf9aaae 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1543,6 +1543,8 @@ static void virt_set_memmap(VirtMachineState *vms)
  */
 static void finalize_gic_version(VirtMachineState *vms)
 {
+    unsigned int max_cpus = MACHINE(vms)->smp.max_cpus;
+
     if (kvm_enabled()) {
         int probe_bitmap;
 
@@ -1583,7 +1585,20 @@ static void finalize_gic_version(VirtMachineState *vms)
             }
             return;
         case VIRT_GIC_VERSION_NOSEL:
-            vms->gic_version = VIRT_GIC_VERSION_2;
+            if ((probe_bitmap & KVM_ARM_VGIC_V2) && max_cpus <= GIC_NCPU) {
+                vms->gic_version = VIRT_GIC_VERSION_2;
+            } else if (probe_bitmap & KVM_ARM_VGIC_V3) {
+                /*
+                 * in case the host does not support v2 in-kernel emulation or
+                 * the end-user requested more than 8 VCPUs we now default
+                 * to v3. In any case defaulting to v2 would be broken.
+                 */
+                vms->gic_version = VIRT_GIC_VERSION_3;
+            } else {
+                error_report("host only supports in-kernel GICv2 emulation "
+                             "but more than 8 vcpus are requested");
+                exit(1);
+            }
             break;
         case VIRT_GIC_VERSION_2:
         case VIRT_GIC_VERSION_3:
-- 
2.20.1