linux-kernel - Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma

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Message-ID: <20190130172653.GA6707@lst.de>
Date:   Wed, 30 Jan 2019 18:26:53 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     "Koenig, Christian" <Christian.Koenig@....com>,
        Christoph Hellwig <hch@....de>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Kuehling, Felix" <Felix.Kuehling@....com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <jroedel@...e.de>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device
 vma

On Wed, Jan 30, 2019 at 10:55:43AM -0500, Jerome Glisse wrote:
> Even outside GPU driver, device driver like RDMA just want to share their
> doorbell to other device and they do not want to see those doorbell page
> use in direct I/O or anything similar AFAICT.

At least Mellanox HCA support and inline data feature where you
can copy data directly into the BAR.  For something like a usrspace
NVMe target it might be very useful to do direct I/O straight into
the BAR for that.