On 1/8/23 22:22, Akihiko Odaki wrote:
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
No need for an ifdef. Down below we have,
if (object_property_find(OBJECT(current_machine), "kvm-type")) {
g_autofree char *kvm_type =
object_property_get_str(OBJECT(current_machine),
"kvm-type",
&error_abort);
type = mc->kvm_type(ms, kvm_type);
} else if (mc->kvm_type) {
type = mc->kvm_type(ms, NULL);
}
and the aarch64 -M virt machine provides virt_kvm_type as mc->kvm_type.
How did you hit this? Are you trying to implement your own board
model?
Looking at this, I'm surprised this is a board hook and not a cpu hook.
But I suppose the architecture specific 'type' can hide any number of
sins. Anyway, if you are doing your own board model, I suggest
arranging to share the virt board hook -- maybe moving it to
target/arm/kvm.c in the process?