linux-kernel - Re: [PATCH v6 0/2] Add p2p via dmabuf to habanalabs

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Date:   Thu, 16 Sep 2021 16:16:03 +0300
From:   Oded Gabbay <ogabbay@...nel.org>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christian König <christian.koenig@....com>,
        Gal Pressman <galpress@...zon.com>,
        Yossi Leybovich <sleybo@...zon.com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Doug Ledford <dledford@...hat.com>,
        Dave Airlie <airlied@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>,
        Christoph Hellwig <hch@....de>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, dsinger@...ana.ai
Subject: Re: [PATCH v6 0/2] Add p2p via dmabuf to habanalabs

On Thu, Sep 16, 2021 at 3:44 PM Oded Gabbay <ogabbay@...nel.org> wrote:
>
> On Thu, Sep 16, 2021 at 3:31 PM Daniel Vetter <daniel@...ll.ch> wrote:
> >
> > Maybe I got the device security model all wrong, but I thought Guadi is
> > single user, and the only thing it protects is the system against the
> > Gaudi device trhough iommu/device gart. So roughly the following can
> > happen:
> >
> > 1. User A opens gaudi device, sets up dma-buf export
> >
> > 2. User A registers that with RDMA, or anything else that doesn't support
> > revoke.
> >
> > 3. User A closes gaudi device
> This can not happen without User A closing the FD of the dma-buf it exported.
> We prevent User A from closing the device because when it exported the
> dma-buf, the driver's code took a refcnt of the user's private
> structure. You can see that in export_dmabuf_common() in the 2nd
> patch. There is a call there to hl_ctx_get.
> So even if User A calls close(device_fd), the driver won't let any
> other user open the device until User A closes the fd of the dma-buf
> object.
>
> Moreover, once User A will close the dma-buf fd and the device is
> released, the driver will scrub the device memory (this is optional
> for systems who care about security).
>
> And AFAIK, User A can't close the dma-buf fd once it registered it
> with RDMA, without doing unregister.
> This can be seen in ib_umem_dmabuf_get() which calls dma_buf_get()
> which does fget(fd)

Adding Daniel, I don't know how his email got dropped when I replied to him...