linux-kernel - Re: [RFC PATCH 00/28] Removing struct page from P2PDMA

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Date:   Mon, 24 Jun 2019 15:50:24 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-pci@...r.kernel.org, linux-rdma <linux-rdma@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <kbusch@...nel.org>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 00/28] Removing struct page from P2PDMA

On Mon, Jun 24, 2019 at 10:46:41AM -0300, Jason Gunthorpe wrote:
> BTW, it is not just offset right? It is possible that the IOMMU can
> generate unique dma_addr_t values for each device?? Simple offset is
> just something we saw in certain embedded cases, IIRC.

Yes, it could.  If we are trying to do P2P between two devices on
different root ports and with the IOMMU enabled we'll generate
a new bus address for the BAR on the other side dynamically everytime
we map.