From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alex Williamson <alex.williamson@redhat.com>
Subject: Re: A question about "CONFIG_KVM_DEVICE_ASSIGNMENT" configuration
Date: Thu, 10 Sep 2015 09:08:36 -0600
Message-ID: <1441897716.20355.565.camel@redhat.com>
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Cc: kvm@vger.kernel.org
To: Nan Xiao <xiaonan830818@gmail.com>
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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
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