[PATCH] accel/kvm: Specify default IPA size for arm64

[Akihiko Odaki]

libvirt uses "none" machine type to test KVM availability. Before this
change, QEMU used to pass 0 as machine type when calling KVM_CREATE_VM.

The kernel documentation says:
> On arm64, the physical address size for a VM (IPA Size limit) is
> limited to 40bits by default. The limit can be configured if the host
> supports the extension KVM_CAP_ARM_VM_IPA_SIZE. When supported, use
> KVM_VM_TYPE_ARM_IPA_SIZE(IPA_Bits) to set the size in the machine type
> identifier, where IPA_Bits is the maximum width of any physical
> address used by the VM. The IPA_Bits is encoded in bits[7-0] of the
> machine type identifier.
>
> e.g, to configure a guest to use 48bit physical address size::
>
>     vm_fd = ioctl(dev_fd, KVM_CREATE_VM, KVM_VM_TYPE_ARM_IPA_SIZE(48));
>
> The requested size (IPA_Bits) must be:
>
>  ==   =========================================================
>   0   Implies default size, 40bits (for backward compatibility)
>   N   Implies N bits, where N is a positive integer such that,
>       32 <= N <= Host_IPA_Limit
>  ==   =========================================================

> Host_IPA_Limit is the maximum possible value for IPA_Bits on the host
> and is dependent on the CPU capability and the kernel configuration.
> The limit can be retrieved using KVM_CAP_ARM_VM_IPA_SIZE of the
> KVM_CHECK_EXTENSION ioctl() at run-time.
>
> Creation of the VM will fail if the requested IPA size (whether it is
> implicit or explicit) is unsupported on the host.
https://docs.kernel.org/virt/kvm/api.html#kvm-create-vm

So if Host_IPA_Limit < 40, such KVM_CREATE_VM will fail, and libvirt
incorrectly thinks KVM is not available. This actually happened on M2
MacBook Air.

Fix this by specifying 32 for IPA_Bits as any arm64 system should
support the value according to the documentation.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 accel/kvm/kvm-all.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index e86c33e0e6..776ac7efcc 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2294,7 +2294,11 @@ static int kvm_init(MachineState *ms)
     KVMState *s;
     const KVMCapabilityInfo *missing_cap;
     int ret;
+#ifdef TARGET_AARCH64
+    int type = 32;
+#else
     int type = 0;
+#endif
     uint64_t dirty_log_manual_caps;
 
     qemu_mutex_init(&kml_slots_lock);
-- 
2.39.0