remove nopage

This patchset removes the 'nopage' from the tree.

I've gone through all the drivers and converted them to use fault as best I can. When using fault, I've also tried to use vmf->pgoff rather than the virtual address to index the content (which is preferred). Mostly it has been OK, but DRM is a bit difficult, as it seems to use vma->vm_pgoff as a 2nd dimension of addressing, so it remains unconverted.

I've also done some other things while going through at the code...

Converted incorrect OOM returns to SIGBUS. OOM should only be returned as a result of a memory allocation failure. We will actually want the fault path OOM handling to be unified with the normal OOM killing path in future, and so OOMing when we should be SIGBUSing means the box will panic if panic_on_oom is set, or it will oom-kill random processes before retrying the fault, etc. SIGBUS means something like "physical address (ie. after translation) does not exist", which is appropriate AFAIKS in all cases I've converted.

Got rid of some bogus looking "disallow mremap" checks that just check for address > vma->vm_end. Presumably this is supposed to prevent an mremap expanding the mapping outside the limit of the underlying resource, but actually mremap will update vma->vm_end, and anyway this condition is already checked in the page fault code. Others seem to get this right by checking the underlying resource itself. Others don't seem to even care.

There looks like a fair number of corruption / security problems with mremap, so I've done an audit of the tree and tried to plug them.