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

[Logan Gunthorpe]

On 19/04/17 01:31 PM, Jason Gunthorpe wrote:
> Try it with VT-D turned on. It shouldn't work or there is a notable
> security hole in your platform..

Ah, ok.

>>> 	 const struct dma_map_ops *comp_ops = get_dma_ops(completer);
>>> 	 const struct dma_map_ops *init_ops = get_dma_ops(initiator);
>>
>> So, in this case, what device does the completer point to? The PCI
>> device or a more specific GPU device? If it's the former, who's
>> responsible for setting the new dma_ops? Typically the dma_ops are arch
>> specific but now you'd be adding ones that are tied to hmm or the gpu.
> 
> Donno, that is for GPU folks to figure out :)
> 
> But.. it could point to a GPU and the GPU struct device could have a
> proxy dma_ops like Dan pointed out.

Seems a bit awkward to me that in order for the intended use case, you
have to proxy the dma_ops. I'd probably still suggest throwing a couple
ops for things like this in the dev_pagemap.

>> It appears to me like it's calculating the DMA address, and the check is
>> just a side requirement. It reads as though it's only doing the check.
> 
> pci_p2p_same_segment_get_pa() then?

Ok, I think that's a bit clearer.

Logan