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

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Message-ID: <20210624053421.GA25165@lst.de>
Date:   Thu, 24 Jun 2021 07:34:21 +0200
From:   Christoph Hellwig <hch@....de>
To:     Oded Gabbay <oded.gabbay@...il.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        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:
> 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.

But the scatterlist is defined to have a valid page.  If in dma-bufs you
can't do that dmabufs are completely broken.  Apparently the gpu folks
can somehow live with that and deal with the pitfals, but for dma-buf
users outside of their little fiefdom were they arbitrarily break rules
it simply is not acceptable.