Disable coherent dumb buffers without 3d to improve graphics performance

Summary

In the Linux kernel, the following vulnerability has been resolved: drm/vmwgfx: Disable coherent dumb buffers without 3d Coherent surfaces make only sense if the host renders to them using accelerated apis. Without 3d the entire content of dumb buffers stays in the guest making all of the extra work they're doing to synchronize between guest and host useless. Configurations without 3d also tend to run with very low graphics memory limits. The pinned console fb, mob cursors and graphical login manager tend to run out of 16MB graphics memory that those guests use. Fix it by making sure the coherent dumb buffers are only used on configs with 3d enabled.