linux-kernel - Re: KVM PCI passthrough problems after kernel v4.2

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Date:	Fri, 13 Nov 2015 06:48:41 +0200
From:	Juhani Rautiainen <jrauti@....fi>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	iommu <iommu@...ts.linux-foundation.org>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: KVM PCI passthrough problems after kernel v4.2

Hi!

Thanks a lot for the help. I switched to vfio and got NIC working
again. Now I just have to figure out what I have to change to get this
to persist through the host boots. To tell the truth I couldn't quite
parse from that commit message that my device would stop working:).
The error messages in this area are quite uninformative anyway. KVM
could for instance warn for using deprecated method (kernel does it in
many other places). When I did that configuration, I did it using KVM
PCI passthrough pages and the method there was this deprecated method
(and it still was when I switched to Centos7, because I lost my config
through stupid mistake and had to do it all over again). And I thought
that I've been following this area in LKML but somehow missed the
whole deprecation business:).

Thanks,
-Juhani

On Fri, Nov 13, 2015 at 12:00 AM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> On Thu, 2015-11-12 at 23:36 +0200, Juhani Rautiainen wrote:
>> Hi!
>>
>> I've been using KVM PCI passthrough with a dual-port NIC for over a
>> year. I just upgraded to v4.3 from v4.1.4 and PCI passthrough stopped
>> working. I checked with v4.1.9 and it still works there. Version 4.2
>> seems to point after which my system doesn't work. How can I help to
>> narrow down the cause of the problem? I checked the intel-iommu.c and
>> there seem to have been lots of changes between 4.1.9 and 4.2 in
>> drivers/iommu/intel-iommu.c. My motherboard is Asus P8C WS which has
>> Intel C216 chipset. CPU is Intel I5-3470. From v4.2 onwards
>> passthrough fails with:
>>
>> pci-stub 0000:02:00.0: kvm assign device failed ret -22.
>
> This happens when kvm calls iommu_attach_device(), which was changed in
> v4.2 to fail with -EINVAL (-22) when the device is part of a
> non-singleton iommu group.  Legacy kvm device assignment is not iommu
> group aware and has been deprecated for some time.  Have you considered
> using vfio for device assignment instead?
>
> For reference, here's the comment that made this change:
>
> commit 426a273834eae65abcfc7132a21a85b3151e0bce
> Author: Joerg Roedel <jroedel@...e.de>
> Date:   Thu May 28 18:41:30 2015 +0200
>
>     iommu: Limit iommu_attach/detach_device to devices with their own group
>
>     This patch changes the behavior of the iommu_attach_device
>     and iommu_detach_device functions. With this change these
>     functions only work on devices that have their own group.
>     For all other devices the iommu_group_attach/detach
>     functions must be used.
>
>     Signed-off-by: Joerg Roedel <jroedel@...e.de>
>
>



-- 
Juhani Rautiainen                                   jrauti@....fi
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