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Date:   Tue, 4 Apr 2017 11:21:58 -0600
From:   Logan Gunthorpe <>
To:     Jason Gunthorpe <>,
        Sagi Grimberg <>
Cc:     Christoph Hellwig <>,
        "James E.J. Bottomley" <>,
        "Martin K. Petersen" <>,
        Jens Axboe <>,
        Steve Wise <>,
        Stephen Bates <>,
        Max Gurtovoy <>,
        Dan Williams <>,
        Keith Busch <>,,,,,,
Subject: Re: [RFC 6/8] nvmet: Be careful about using iomem accesses when
 dealing with p2pmem

On 04/04/17 04:59 AM, Sagi Grimberg wrote:
> We can never ever get here from an IO command, and that is a good thing
> because it would have been broken if we did, regardless of what copy
> method we use...

Yes, I changed this mostly for admin commands. I did notice connect
commands do end up reading from the p2mem and this patchset correctly
switches it to iomemcpy. However, based on Cristoph's comment, I hope to
make it more general such that iomem is hidden within sgls and any
access will either be correct or create a warning.

On 04/04/17 09:46 AM, Jason Gunthorpe wrote:
> Transactions might not complete at the NVMe device before the CPU
> processes the RDMA completion, however due to the PCI-E ordering rules
> new TLPs directed to the NVMe will complete after the RMDA TLPs and
> thus observe the new data. (eg order preserving)
> It would be very hard to use P2P if fabric ordering is not preserved..

Yes, my understanding is the same, the PCI-E ordering rules save us here.



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