[PATCH] dma-buf: Require VM_PFNMAP vma for mmap

[Daniel Vetter]

On Tue, 22 Nov 2022 at 20:34, Jason Gunthorpe <jgg at ziepe.ca> wrote:
> On Tue, Nov 22, 2022 at 08:29:05PM +0100, Daniel Vetter wrote:
> > You nuke all the ptes. Drivers that move have slightly more than a
> > bare struct file, they also have a struct address_space so that
> > invalidate_mapping_range() works.
>
> Okay, this is one of the ways that this can be made to work correctly,
> as long as you never allow GUP/GUP_fast to succeed on the PTEs. (this
> was the DAX mistake)

Hence this patch, to enforce that no dma-buf exporter gets this wrong.
Which some did, and then blamed bug reporters for the resulting splats
:-) One of the things we've reverted was the ttm huge pte support,
since that doesn't have the pmd_special flag (yet) and so would let
gup_fast through.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch