![]() ![]() Ugh.įortunately, Alex has also written kernel patches to fix this, however be warned that they cripple 3D performance on the Intel GPU. This means VGA calls get directed to the wrong card, (a) messing up your display on the host and (b) preventing the graphics card on the VM from functioning correctly. ![]() The problem is that the Xorg i915 driver for Intel's integrated GPUs does not participate in VGA arbitration, even though the devices claim the VGA address space. In short, the x-vga=on flag passed to VFIO indicates to the VGA arbiter that the VFIO driver will need to participate in VGA arbitration, so everyone stays happy. I am oversimplifying this a bit, but Alex Williamson has a detailed post explaining the technical issues. VGA calls can only be directed to a single device at a time, so the kernel has to use a VGA arbiter that switches the active device and directs VGA accesses to the appropriate card. Back when it was created, having multiple graphics cards on a single system was not a configuration they had foreseen or designed for. This will be a major headache when trying to setup VGA passthrough, as VGA is a really old standard. Most computers today come with a GPU built-in to the CPU. Graphics card passthrough gets put into its own category called "VGA passthrough" because of the technical challenges involved in presenting a functioning GPU for the virtual machine to initialize without things going awry. Passing through generic PCI devices with VFIO works pretty well. Without this extra PCIe reset support, the machine typically freezes when starting your VM for a second time.įortunately for us, kernel >= 3.12 has this support and simply upgrading the kernel fixes the issue. Normally the host controls this, however now that we are passing through the device to a VM, some additional work is required to get reset functioning correctly. In order to re-initialize a PCIe device, it needs to be reset. Understanding these issues will be key in creating a functioning host environment for VFIO VGA passthrough. Common problems with VGA VFIO passthroughīefore getting to the fun part, there are several key pieces to getting a functioning VGA passthrough that need further description. From my reading nVidia's GeForce 6xx/7xx and AMD's Radeon R9 series seem to work fairly painlessly.įor network cards, always pass through an Intel ethernet controller over a Realtek one if possible. applying certain patches) to get a compatible passthrough. I have found that generally, problems are not inherent to the hardware but more a matter of adjusting you software stack (i.e. However, success has been had on both sides on a variety of device models dating back several years. Audio: Onboard (Intel C220 HD audio) and AMD R9 270X HDMIĪnecdotal evidence suggests that for graphics passthrough, nVidia cards seem to fare better than AMD ones.Personally, the following hardware has worked wonderfully for me: If you are purchasing hardware, it is also strongly recommended that you read over the KVM VGA-passthrough thread on Arch Forums to confirm that your intended hardware configuration has been reported to work by another user. Likely, until Fedora 21 is released you will need to patch and rebuild both the Linux kernel and QEMU instructions for doing so will be provided in this tutorial. While myself and many others have had tremendous success, different hardware can produce different results and getting there may not always be straightforward. That said, VFIO it is relatively new and experimental technology for the purposes of passing through entire VGA cards to virtual machines. QEMU's normal PCI passthrough leaves much to be desired whereas VFIO takes full advantage of IOMMU, has better device support and prevents multiple access to the same device (you can read more about it in Alex Williamson's presentation here). QEMU has several PCI passthrough techniques, the newest of which is VFIO. Configure CPU pinning on the VM for better gaming performance.Create and configure a new virtual machine (VM) with real hardware attached to it.Patch the kernel and QEMU for better compatibility with graphics card / VGA VFIO passthrough.Install and configure the KVM hypervisor.This how-to will show you how to configure: ![]()
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