Marek Olšák has implemented support for the GL_AMD_pinned_memory extension within Mesa/Gallium3D and the R600g and RadeonSI Gallium3D drivers.

Per the OpenGL.org registry, "This extension defines an interface that allows improved control of the physical memory used by the graphics device. It allows an existing page of system memory allocated by the application to be used as memory directly accessible to the graphics processor. One example application of this functionality would be to be able to avoid an explicit synchronous copy with sub-system of the application; for instance it is possible to directly draw from a system memory copy of a video image."

This modern AMD OpenGL extension for pinned memory was implemented over six patches and does depend on Userptr support, so you'll need a relatively recent kernel as well.