Alex:
Thanks for your quick reply and the information. One question though:
When you say contact the platform vendor, are you talking about the
vendor of the GPU card (NVidia) or the vendor of the system hardware
(HP)? I.E. is the problem in the system BIOS/firmware or in the firmware
of the GPU card?
This seems like this is going to be the death-knell of PCI passthrough
as the likelihood of getting a system vendor to fix some obscure thing
like this seems remote.
On 03/06/2015 01:10 AM, Alex Williamson wrote:
On Fri, 2015-03-06 at 00:20 -0500, Steven DuChene wrote:
I am attempting on ubuntu 14.04 to configure PCI passthrough of a NVidia
K40 GPU card that is plugged into a HP DL580 rack mounted server.
I have done all of the pre-work I normally have done in the past with
pci-stub, vfio and etc but when I try an execute a qemu-system-x86_64
command that works on a similar version of debian, I get the following
error in the dmesg:
Device is ineligible for IOMMU domain attach due to platform RMRR
requirement. Contact your platform vendor.
I have read through the patch description from Alex at:
http://lists.linuxfoundation.org/pipermail/iommu/2014-June/008816.html
and I have read the IOMMU documentation at:
https://www.kernel.org/doc/Documentation/Intel-IOMMU.txt
but I am still not really understanding if or what the fix is for this.
The ubuntu 14.04 system where I am getting this error is running
3.16.0-30-generic
The debian system where I can do similar PCI passthrough of a NVidia K2
GPU device is running a 3.14.29-4 kernel.
Can anyone provide any insight into an fix or workaround for this?
Hi Steven,
The issue is that VT-d RMRRs are a platform imposed requirement that a
device continue to have identity mapped access to a platform defined
memory region at all times. This requirement is fundamentally
incompatible with PCI device assignment where the address space of the
assigned device is defined by the VM. The VT-d specification hints at
this restriction (8.4):
The RMRR regions are expected to be used for legacy usages (such
as USB, UMA Graphics, etc.) requiring reserved memory. Platform
designers should avoid or limit use of reserved memory regions
since these require system software to create holes in the DMA
virtual address range available to system software and its
drivers.
In order to support assignment of such devices and continue to honor the
RMRR, reserved memory regions would need to be imposed on the guest.
Doing this has a number of issues and it's not clear that it enables any
usable configurations due to the lack of isolation often implied by the
RMRRs. RMRRs themselves imply some sort of communication conduit to the
platform, which it's also not clear should be allowed for a guest owned
device.
We also cannot continue the previous behavior of simply ignoring RMRRs
for assigned devices. Not only does the platform require us to honor
them, failing to do so could have implication for both the platform and
the VM health and integrity.
As indicated by the dmesg warning, users encountering this problem
should contact their platform vendor, which is really the only course of
action that I can recommend. Only the platform vendor can tell you why
they've imposed this requirement for the device and potentially offer a
remedy to remove that requirement. KVM is not the first hypervisor to
impose this restriction for such devices. The referenced patch was
tagged for stable, so you can expect that this change will eventually
trickle through all the distributions. Sorry for the trouble, but it
really was a necessary change. Thanks,
Alex
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