Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

[Dan Williams]

On Tue, Apr 18, 2017 at 12:35 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:
>
>
> On 18/04/17 01:01 PM, Jason Gunthorpe wrote:
>> Ultimately every dma_ops will need special code to support P2P with
>> the special hardware that ops is controlling, so it makes some sense
>> to start by pushing the check down there in the first place. This
>> advice is partially motivated by how dma_map_sg is just a small
>> wrapper around the function pointer call...
>
> Yes, I noticed this problem too and that makes sense. It just means
> every dma_ops will probably need to be modified to either support p2p
> pages or fail on them. Though, the only real difficulty there is that it
> will be a lot of work.

I don't think you need to go touch all dma_ops, I think you can just
arrange for devices that are going to do dma to get redirected to a
p2p aware provider of operations that overrides the system default
dma_ops. I.e. just touch get_dma_ops().