On Thu, 23 Jul 2020 21:38:31 +0000 Ross Deleon <rdeleon@xxxxxxxxxxx> 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
