VFIO Adds Sample Mediated Device Display Drivers

The VFIO framework that allows exposing direct device access to user-space in a secure, IOMMU-protected fashion is gaining some new sample drivers in Linux 4.18.

VFIO has been a popular topic recently especially for discrete GPUs in order to get a dedicated graphics processor assigned directly to a (Windows) virtual machine so that it can be driven for a performant gaming experience. The VFIO Mediated Device capability that is part of this framework is for supporting DMA devices that lack SR-IOV support and to support them in a more unified manner (additional background information on VFIO mediated devices via the kernel documentation).

With the Linux 4.18 kernel there are new VFIO mediated device "mdev" sample drivers. These sample drivers include building a virtual display driver with a simple frame-buffer, an example guest frame-buffer device (fbdev) driver, and another sample driver that is enough to satisfy the Bochs DRM/KMS driver. Hopefully this sample code will be useful for developers new to the Linux kernel VFIO APIs for developing real mediated device drivers.

The VFIO updates for Linux 4.18 also include a change for vCPU hot-plugging within QEMU, better error message consistency for the VFIO platform code, and various fixes.