[Beignet] [Intel-gfx] Preventing zero GPU virtual address allocation

[Chris Wilson]

On Mon, Mar 09, 2015 at 02:34:46AM +0000, Zou, Nanhai wrote:
> We don't need MAP_FIXED, we just want to avoid address 0 to be allocated.
> 
> Though I think using MAP_FIXED is overkill, will bring much unnecessary complexity on both kernel and beignet side.
> I don't mind if people can provide stable MAP_FIXED patches to resolve this problem a few months or years later.
> 
> At that time, kernel driver can revert the reserve page 0 patch.
> Before that reserve page 0 can benefit all the Beignet user without breaking anything.

The point is that is becomes ABI. So no the kernel can't just revert it.
There is nothing special about address 0 in ether GTT or virtual memory.
If you require a special object allocated at address 0, allocate a
special object at address 0.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre