Re: A question about "CONFIG_KVM_DEVICE_ASSIGNMENT" configuration

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 9/10/2015 11:08 PM, Alex Williamson wrote:
> On Thu, 2015-09-10 at 18:22 +0800, Nan Xiao wrote:
>> Hi all,
>>
>> When building kernel, it prompts "CONFIG_KVM_DEVICE_ASSIGNMENT" is "deprecated".
>> But it is still used in kernel code. E.g.:
>> "kvm_vm_ioctl_check_extension" function:
>> {
>>     ...
>> #ifdef CONFIG_KVM_DEVICE_ASSIGNMENT
>> case KVM_CAP_ASSIGN_DEV_IRQ:
>> case KVM_CAP_PCI_2_3:
>> #endif
>> r = 1;
>> break;
>>    ...
>> #ifdef CONFIG_KVM_DEVICE_ASSIGNMENT
>> case KVM_CAP_IOMMU:
>> r = iommu_present(&pci_bus_type);
>> break;
>> #endif
>>    ...
>> }
>>
>> If not configure this option, the following code will execute failed:
>>
>>     ret = ioctl(dev, KVM_CHECK_EXTENSION, KVM_CAP_IOMMU);
>>
>> So does it mean to use KVM assigned device feature, the
>> "CONFIG_KVM_DEVICE_ASSIGNMENT"
>> is not "deprecated"?
>
> Legacy KVM device assignment is deprecated, it is fully replaced by

Why do we remove this legacy assignment completely? Its always leading 
to this confusion :)

Thanks
Tiejun

> VFIO-based device assignment.  The intention is to deprecate legacy KVM
> device assignment now, so all users can transition away from it and at
> some point remove it from the kernel.  When using QEMU and libvirt, the
> default is already to use VFIO instead of legacy KVM device assignment.
> Thanks,
>
> Alex