Re: [PATCH v3 05/12] drm/ttm: Expose ttm_tt_unpopulate for driver use

On 2020-11-25 1:57 p.m., Christian König wrote:

Well thinking more about this, it seems to be a another really good argument why mapping pages from DMA-bufs into application address space directly is a very bad idea :)

Apologies for going off on a tangent here...

Since allowing userspace mmap with dma-buf fds seems to be a trap in general[0], I wonder if there's any way we could stop supporting that?

[0] E.g. mutter had to disable handing out dma-bufs for screen capture by default with non-i915 for now, because in particular with discrete GPUs, direct CPU reads can be unusably slow (think single-digit frames per second), and of course there's other userspace which goes "ooh, dma-buf, let's map and read!".