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Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings |
Date: |
Fri, 26 Aug 2011 10:29:00 -0500 |
On 26.08.2011, at 10:24, Joerg Roedel wrote:
> On Fri, Aug 26, 2011 at 09:07:35AM -0500, Alexander Graf wrote:
>> On 26.08.2011, at 04:33, Roedel, Joerg wrote:
>>>
>>> The reason is that you mean the usability for the programmer and I mean
>>> it for the actual user of qemu :)
>>
>> No, we mean the actual user of qemu. The reason being that making a
>> device available for any user space application is an administrative
>> task.
>>
>> Forget the KVM case for a moment and think of a user space device
>> driver. I as a user am not root. But I as a user when having access to
>> /dev/vfioX want to be able to access the device and manage it - and
>> only it. The admin of that box needs to set it up properly for me to
>> be able to access it.
>
> Right, and that task is being performed by attaching the device(s) in
> question to the vfio driver. The rights-management happens on the
> /dev/vfio/$group file.
Yup :)
>
>> So having two steps is really the correct way to go:
>>
>> * create VFIO group
>> * use VFIO group
>>
>> because the two are done by completely different users. It's similar
>> to how tun/tap works in Linux too. Of course nothing keeps you from
>> also creating a group on the fly, but it shouldn't be the only
>> interface available. The persistent setup is definitely more useful.
>
> I see the use-case. But to make it as easy as possible for the end-user
> we can do both.
>
> So the user of (qemu again) does this:
>
> # vfio-ctl attach 00:01.0
> vfio-ctl: attached to group 8
> # vfio-ctl attach 00:02.0
> vfio-ctl: attached to group 16
> $ qemu -device vfio-pci,host=00:01.0 -device vfio,host=00:01.0 ...
>
> which should cover the usecase you prefer. Qemu still creates the
> meta-group that allow the devices to share the same page-table. But what
> should also be possible is:
>
> # qemu -device vfio-pci,host=00:01.0 -device vfio-pci,host=00:02.0
>
> In that case qemu detects that the devices are not yet bound to vfio and
> will do so and also unbinds them afterwards (essentially the developer
> use-case).
I agree. The same it works with tun today. You can either have qemu spawn a tun
device dynamically or have a preallocated one you use. If you run qemu as a
user (which I always do), I preallocate a tun device and attach qemu to it.
> Your interface which requires pre-binding of devices into one group by
> the administrator only makes sense if you want to force userspace to
> use certain devices (which do not belong to the same hw-group) only
> together. But I don't see a usecase for defining such constraints (yet).
Agreed. As long as the kernel backend can always figure out the hw-groups,
we're good :)
Alex
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, (continued)
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Joerg Roedel, 2011/08/30
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Joerg Roedel, 2011/08/23
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, aafabbri, 2011/08/23
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/24
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, David Gibson, 2011/08/24
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/24
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, David Gibson, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Alexander Graf, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Joerg Roedel, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings,
Alexander Graf <=
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Aaron Fabbri, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Chris Wright, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Aaron Fabbri, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Chris Wright, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, David Gibson, 2011/08/29
Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Joerg Roedel, 2011/08/04