linux-kernel - Re: [PATCH 1/2] mm: introduce put_user

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Date:   Wed, 12 Dec 2018 20:26:37 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>, Jan Kara <jack@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        John Hubbard <john.hubbard@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, tom@...pey.com,
        Al Viro <viro@...iv.linux.org.uk>, benve@...co.com,
        Christoph Hellwig <hch@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        "Dalessandro, Dennis" <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        rcampbell@...dia.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "Weiny, Ira" <ira.weiny@...el.com>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions

On Wed, Dec 12, 2018 at 07:44:37PM -0500, Jerome Glisse wrote:

> On many GPUs you can do that, it is hardware dependant and you have
> steps to take but it is something you can do (and GPU can do
> continuous DMA traffic have they have threads running that can
> do continuous memory access). So i assume that other hardware
> can do it too.

RDMA has no generic way to modify a MR and then guarntee the HW sees
the modifications. Some HW can do this (ie the same HW that can do
ODP, because ODP needs this capability), other HW is an unknown as
this has never been asked for as a driver API.

Jason