linux-kernel - Re: [PATCH v2 10/17] media/videbuf1|2: Mark follow

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Date:   Sat, 10 Oct 2020 11:24:16 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-media@...r.kernel.org,
        linux-s390@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>, Pawel Osciak <pawel@...iak.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Michel Lespinasse <walken@...gle.com>
Subject: Re: [PATCH v2 10/17] media/videbuf1|2: Mark follow_pfn usage as
 unsafe

Em Fri,  9 Oct 2020 09:59:27 +0200
Daniel Vetter <daniel.vetter@...ll.ch> escreveu:

> 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.

I won't repeat here the discussions for patch 09/17, but
just to be clear about this one:

NACK.

We need a better alternative to avoid breaking existing
media applications.

> 
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: linux-mm@...ck.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-samsung-soc@...r.kernel.org
> Cc: linux-media@...r.kernel.org
> Cc: Pawel Osciak <pawel@...iak.com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Kyungmin Park <kyungmin.park@...sung.com>
> Cc: Tomasz Figa <tfiga@...omium.org>
> Cc: Laurent Dufour <ldufour@...ux.ibm.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Daniel Jordan <daniel.m.jordan@...cle.com>
> Cc: Michel Lespinasse <walken@...gle.com>
> ---
>  drivers/media/common/videobuf2/frame_vector.c | 2 +-
>  drivers/media/v4l2-core/videobuf-dma-contig.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
> index 2b0b97761d15..a1b85fe9e7c1 100644
> --- a/drivers/media/common/videobuf2/frame_vector.c
> +++ b/drivers/media/common/videobuf2/frame_vector.c
> @@ -69,7 +69,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
>  			break;
>  
>  		while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
> -			err = follow_pfn(vma, start, &nums[ret]);
> +			err = unsafe_follow_pfn(vma, start, &nums[ret]);
>  			if (err) {
>  				if (ret == 0)
>  					ret = err;
> diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
> index 52312ce2ba05..821c4a76ab96 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
> @@ -183,7 +183,7 @@ static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory *mem,
>  	user_address = untagged_baddr;
>  
>  	while (pages_done < (mem->size >> PAGE_SHIFT)) {
> -		ret = follow_pfn(vma, user_address, &this_pfn);
> +		ret = unsafe_follow_pfn(vma, user_address, &this_pfn);
>  		if (ret)
>  			break;
>  



Thanks,
Mauro