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Message-ID: <ea03e81f-e3d5-9f5c-db60-0ceaf4366612@deltatee.com>
Date: Wed, 19 Apr 2017 13:41:49 -0600
From: Logan Gunthorpe <logang@...tatee.com>
To: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Dan Williams <dan.j.williams@...el.com>,
Bjorn Helgaas <helgaas@...nel.org>,
Christoph Hellwig <hch@....de>,
Sagi Grimberg <sagi@...mberg.me>,
"James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Jens Axboe <axboe@...nel.dk>,
Steve Wise <swise@...ngridcomputing.com>,
Stephen Bates <sbates@...thlin.com>,
Max Gurtovoy <maxg@...lanox.com>,
Keith Busch <keith.busch@...el.com>, linux-pci@...r.kernel.org,
linux-scsi <linux-scsi@...r.kernel.org>,
linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
linux-nvdimm <linux-nvdimm@...1.01.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Jerome Glisse <jglisse@...hat.com>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
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
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