linux-kernel - Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 23 Jun 2021 16:34:56 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Oded Gabbay <oded.gabbay@...il.com>
Cc:     Christian König <ckoenig.leichtzumerken@...il.com>,
        Christian König <christian.koenig@....com>,
        Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Oded Gabbay <ogabbay@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        Doug Ledford <dledford@...hat.com>,
        Tomer Tayar <ttayar@...ana.ai>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export
 FD for DMA-BUF

On Wed, Jun 23, 2021 at 10:00:29PM +0300, Oded Gabbay wrote:
> On Wed, Jun 23, 2021 at 9:50 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
> >
> > On Wed, Jun 23, 2021 at 09:43:04PM +0300, Oded Gabbay wrote:
> >
> > > Can you please explain why it is so important to (allow) access them
> > > through the CPU ?
> >
> > It is not so much important, as it reflects significant design choices
> > that are already tightly baked into alot of our stacks.
> >
> > A SGL is CPU accessible by design - that is baked into this thing and
> > places all over the place assume it. Even in RDMA we have
> > RXE/SWI/HFI1/qib that might want to use the CPU side (grep for sg_page
> > to see)
> >
> > So, the thing at the top of the stack - in this case the gaudi driver
> > - simply can't assume what the rest of the stack is going to do and
> > omit the CPU side. It breaks everything.
> >
> > Logan's patch series is the most fully developed way out of this
> > predicament so far.
> 
> I understand the argument and I agree that for the generic case, the
> top of the stack can't assume anything.
> Having said that, in this case the SGL is encapsulated inside a dma-buf object.
>
> Maybe its a stupid/over-simplified suggestion, but can't we add a
> property to the dma-buf object,
> that will be set by the exporter, which will "tell" the importer it
> can't use any CPU fallback ? Only "real" p2p ?

The block stack has been trying to do something like this.

The flag doesn't solve the DMA API/IOMMU problems though.

Jason