A set of 26 patches against Mesa were needed for this initial ARB_texture_multisample implementation. The only driver implementing the support with these patches is the Intel DRI driver and even there it's only on right now for Intel Sandy Bridge "Gen6" hardware. For the newer Ivy Bridge "Gen7", there's still some IVB-specific things that aren't done or properly tested. Even for Sandy Bridge with these patches, there's some HiZ interactions that are likely wrong along with some other likely issues.
The GL_ARB_texture_multisample extension is part of the OpenGL 3.2 specification. Per the OpenGL.org registry, this NVIDIA-developed extension is described as:
This extension provides support for two new types of "multisample textures" - two-dimensional and two-dimensional array - as well as mechanisms to fetch a specific sample from such a texture in a shader, and to attach such textures to FBOs for rendering. This extension also includes the following functionality, first described in NV_explicit_multisample:Hopefully these patches can be cleaned up soon for the Intel driver, expanded eventually to support the Nouveau and Radeon Gallium3D drivers, and be merged into mainline Mesa ahead of the next Mesa 9.1/10.0 release. The current set of 26 patches can be found in this mailing list thread.
* A query in the API to query the location of samples within the pixel
* An explicit control for the multisample sample mask to augment the control provided by SampleCoverage