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Date:   Tue, 16 Mar 2021 15:45:49 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Daniel Vetter <daniel.vetter@ffwll.ch>
Cc:     DRI Development <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org,
        linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org,
        Tomasz Figa <tfiga@chromium.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Kees Cook <keescook@chromium.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        John Hubbard <jhubbard@nvidia.com>,
        J??r??me Glisse <jglisse@redhat.com>, Jan Kara <jack@suse.cz>,
        Pawel Osciak <pawel@osciak.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Michel Lespinasse <walken@google.com>
Subject: Re: [PATCH 2/3] media/videobuf1|2: Mark follow_pfn usage as unsafe
Message-ID: <20210316154549.GA60450@infradead.org>
References: <20210316153303.3216674-1-daniel.vetter@ffwll.ch>
 <20210316153303.3216674-3-daniel.vetter@ffwll.ch>
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On Tue, Mar 16, 2021 at 04:33:02PM +0100, Daniel Vetter wrote:
> The media model assumes that buffers are all preallocated, so that
> when a media pipeline is running we never miss a deadline because the
> buffers aren't allocated or available.
> 
> This means we cannot fix the v4l follow_pfn usage through
> mmu_notifier, without breaking how this all works. The only real fix
> is to deprecate userptr support for VM_IO | VM_PFNMAP mappings and
> tell everyone to cut over to dma-buf memory sharing for zerocopy.
> 
> userptr for normal memory will keep working as-is, this only affects
> the zerocopy userptr usage enabled in 50ac952d2263 ("[media]
> videobuf2-dma-sg: Support io userptr operations on io memory").

Maybe I'm missing something, but wasn't the conclusion last time that
this hackish early device to device copy support can just go away?