Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM

[Jason Gunthorpe]

On Mon, Oct 05, 2020 at 08:16:33PM +0200, Daniel Vetter wrote:

> > kvm is some similar hack added for P2P DMA, see commit
> > add6a0cd1c5ba51b201e1361b05a5df817083618. It might be protected by notifiers..
> 
> Yeah my thinking is that kvm (and I think also vfio, also seems to
> have mmu notifier nearby) are ok because of the mmu notiifer. Assuming
> that one works correctly.

vfio doesn't have a notifier, Alex was looking to add a vfio private
scheme in the vma->private_data:

https://lore.kernel.org/kvm/159017449210.18853.15037950701494323009.stgit@xxxxxxxxxx/

Guess it never happened.

> > So, the answer really is that s390 and media need fixing, and this API
> > should go away (or become kvm specific)
> 
> I'm still not clear how you want fo fix this, since your vma->dma_buf
> idea is kinda a decade long plan and so just not going to happen:

Well, it doesn't mean we have to change every part of dma_buf to
participate in this. Just the bits media cares about. Or maybe it is
some higher level varient on top of dma_buf.

Or don't use dma_buf for this, add a new object that just provides
refcounts and P2P DMA connection for IO pfn ranges..

Jason