[Intel-gfx] [CI, v3, 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Guenter Roeck]

On Thu, Feb 28, 2019 at 10:18:32PM +0000, Chris Wilson wrote:
> 
> If you have userspace that is broken, we need to fix it. We can get away
> with quietly changing ABI only so long as nobody notices. It sounds like
> you have some userspace that will break if you updated the kernel; ergo
> we have a problem.
> 
> We just need that as a clear statement so that we have the user impact
> recorded.

Yes, it does break our userspace code. I fixed the problem in our kernels
with the following patch:

-	return vma->vm_start == addr && (vma->vm_end - vma->vm_start) == size;
+	return vma->vm_start == addr && (vma->vm_end - vma->vm_start) == roundup(size, PAGE_SIZE);

Guenter