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Date:   Thu, 30 Aug 2018 13:30:32 -0600
From:   Logan Gunthorpe <>
To:     Jerome Glisse <>
        Stephen Bates <>,
        Christoph Hellwig <>,
        Keith Busch <>,
        Sagi Grimberg <>,
        Bjorn Helgaas <>,
        Jason Gunthorpe <>,
        Max Gurtovoy <>,
        Dan Williams <>,
        Benjamin Herrenschmidt <>,
        Alex Williamson <>,
        Christian K├Ânig <>
Subject: Re: [PATCH v5 00/13] Copy Offload in NVMe Fabrics with P2P PCI Memory

On 30/08/18 01:20 PM, Jerome Glisse wrote:
> On Thu, Aug 30, 2018 at 12:53:39PM -0600, Logan Gunthorpe wrote:
> [...]
>> When the PCI P2PDMA config option is selected the ACS bits in every
>> bridge port in the system are turned off to allow traffic to
>> pass freely behind the root port. At this time, the bit must be disabled
>> at boot so the IOMMU subsystem can correctly create the groups, though
>> this could be addressed in the future. There is no way to dynamically
>> disable the bit and alter the groups.

Oh, sorry this paragraph in the cover letter is wrong now. We now rely
on the disable_acs_redir command line option introduced in

aaca43fda742 ("PCI: Add "pci=disable_acs_redir=" parameter for
peer-to-peer support")

> Can you provide an example on how to test this ? Like kernel command
> line option, the doc patch does not have any such example. It would be
> nice to add.

Do you mean to test the patchset or the ACS bits you quoted?

Testing the patchset is a matter of having the right hardware (ie an
RDMA NIC and CMB enabled NVMe behind a PCIe switch, with the ACS bits
set correctly by the above command line option) and setting the p2pmem
configfs attribute in an nvme-of port to 'yes'.


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