Comment 10 for bug 686692

Ok, so it was the right place but a completely wrong explanation. The problem is not that the last part of pointers is missed but that it is not. The problem is that the kernel is given a flat array of address pointers by the domain constructor along with the number of pointer in that array. With recent changes, the Xen kernel code tries to map this into a 3-level tree structure, where the leaves contain a part of that array. To conserve memory, the 2nd level points directly at parts of the flat array, which is ok as long as the whole 4k area is containing valid pointers. But for memory assignments which are not a multiple of 4MB (or 2MB for 64bit) the last leaf would contain some undefined pointers instead of invalid markers.

The attached patch assumes that it is not good to meddle with the memory at the end of the external array, so if there is a final leaf that would only be partially filled, it allocates a new page, initializes it and then copies the valid pointers from the original array.