* Could multiple PCIe devices in one IOMMU group be added to different KVM VM separately?
@ 2020-07-23 21:38 Ross Deleon
2020-07-23 21:55 ` Alex Williamson
0 siblings, 1 reply; 2+ messages in thread
From: Ross Deleon @ 2020-07-23 21:38 UTC (permalink / raw)
To: kvm@vger.kernel.org
Hi:
I want to know could multiple PCIe devices in one IOMMU group be added to different KVM VM separately?
Mother board: ASUS 390-A(intel supports VT-D)
host OS: Ubuntu 18.04 with kernel 4.18.0-15
KVM-QEMU: version 2.11.1
I have got failed message like *card1 is used by VM1, and card2 is in the card1's group and added to VM2, then VM2 can't boot*
I have tried vfio driver, but it didn't work, so what should I do? try SR-IOV? or update KVM-QEMU or update kernel?
Thanks
Dahui
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Could multiple PCIe devices in one IOMMU group be added to different KVM VM separately?
2020-07-23 21:38 Could multiple PCIe devices in one IOMMU group be added to different KVM VM separately? Ross Deleon
@ 2020-07-23 21:55 ` Alex Williamson
0 siblings, 0 replies; 2+ messages in thread
From: Alex Williamson @ 2020-07-23 21:55 UTC (permalink / raw)
To: Ross Deleon; +Cc: kvm@vger.kernel.org
On Thu, 23 Jul 2020 21:38:31 +0000
Ross Deleon <rdeleon@marvell.com> wrote:
> Hi:
> I want to know could multiple PCIe devices in one IOMMU group be
> added to different KVM VM separately? Mother board: ASUS 390-A(intel
> supports VT-D) host OS: Ubuntu 18.04 with kernel 4.18.0-15
> KVM-QEMU: version 2.11.1
> I have got failed message like *card1 is used by VM1, and card2 is in
> the card1's group and added to VM2, then VM2 can't boot* I have tried
> vfio driver, but it didn't work, so what should I do? try SR-IOV? or
> update KVM-QEMU or update kernel?
No. The IOMMU group is the smallest set of devices that are DMA
isolated from other groups. An IOMMU group is the unit of assignment
for vfio and also the granularity with which we manage IOMMU context.
The processor and chipset support for PCIe ACS (Access Control Services)
plays a significant role in getting the smallest granularity in IOMMU
grouping. Consumer systems often do not support ACS to the same degree
as a server, therefore if you have independent devices that are grouped
together, the supported answer might be to get new hardware, or
possibly move the device to a different slot. Intel consumer CPUs do
not support ACS, but the chipsets do make use of several quirks that
can sometime provide ACS equivalent isolation. Thanks,
Alex
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