On Thu, 27 Jul 2023 at 08:31, Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote: > > Before this change, the default KVM type, which is used for non-virt > machine models, was 0. > > 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, specifying 0 as the type will fail. This > actually confused libvirt, which uses "none" machine model to probe the > KVM availability, on M2 MacBook Air. > > Fix this by using Host_IPA_Limit as the default type when > KVM_CAP_ARM_VM_IPA_SIZE is available. > > Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> Reviewed-by: Peter Maydell <peter.maydell@xxxxxxxxxx> thanks -- PMM
