From: Alex Williamson <alex.williamson@redhat.com>
To: Nan Xiao <xiaonan830818@gmail.com>
Cc: kvm@vger.kernel.org
Subject: Re: A question about "CONFIG_KVM_DEVICE_ASSIGNMENT" configuration
Date: Thu, 10 Sep 2015 18:18:07 -0600 [thread overview]
Message-ID: <1441930687.20355.658.camel@redhat.com> (raw)
In-Reply-To: <CA+MhoaNfBO=y-5VMz7gNsZc0RUp1YSuEYHOjGwP=DXj0wbYkOw@mail.gmail.com>
On Fri, 2015-09-11 at 07:58 +0800, Nan Xiao wrote:
> Hi Alex,
>
> Thanks very much for your response! so for assigning PCI device in QEMU.
> The following method is deprecated:
>
> qemu-system-x86_64 ... -device pci-assign,host=0000:21:00.1
>
> I should use this one instead:
>
> qemu-system-x86_64 ... -device vfio-pci,host=0000:21:00.1
>
> right?
Yes, and the device needs to be bound to the vfio_pci driver in the host
rather than pci-stub (and you may or may not need to care about IOMMU
groups[1]). Thanks,
Alex
[1] http://vfio.blogspot.com/2014/08/iommu-groups-inside-and-out.html
> On Thu, Sep 10, 2015 at 11:08 PM, Alex Williamson
> <alex.williamson@redhat.com> 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
> > 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
> >
> >
> >
> --
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next prev parent reply other threads:[~2015-09-11 0:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-10 10:22 A question about "CONFIG_KVM_DEVICE_ASSIGNMENT" configuration Nan Xiao
2015-09-10 15:08 ` Alex Williamson
2015-09-10 23:58 ` Nan Xiao
2015-09-11 0:18 ` Alex Williamson [this message]
2015-09-11 0:42 ` Nan Xiao
2015-09-11 0:55 ` Chen, Tiejun
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