From: Jason Gunthorpe <jgg@ziepe.ca>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "DRI Development" <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"John Hubbard" <jhubbard@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Dan Williams" <dan.j.williams@intel.com>,
"Linux MM" <linux-mm@kvack.org>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
"Pawel Osciak" <pawel@osciak.com>,
"Marek Szyprowski" <m.szyprowski@samsung.com>,
"Kyungmin Park" <kyungmin.park@samsung.com>,
"Tomasz Figa" <tfiga@chromium.org>,
"Inki Dae" <inki.dae@samsung.com>,
"Joonyoung Shim" <jy0922.shim@samsung.com>,
"Seung-Woo Kim" <sw0312.kim@samsung.com>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
"Oded Gabbay" <oded.gabbay@gmail.com>
Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM
Date: Sun, 4 Oct 2020 09:50:59 -0300 [thread overview]
Message-ID: <20201004125059.GP9916@ziepe.ca> (raw)
In-Reply-To: <CAKMK7uFP-XQHUPYeRhPx7tjvjARQiF-os9z9jx6WANV6sgSf6g@mail.gmail.com>
On Sat, Oct 03, 2020 at 11:40:22AM +0200, Daniel Vetter wrote:
> > That leaves the only interesting places as vb2_dc_get_userptr() and
> > vb2_vmalloc_get_userptr() which both completely fail to follow the
> > REQUIRED behavior in the function's comment about checking PTEs. It
> > just DMA maps them. Badly broken.
> >
> > Guessing this hackery is for some embedded P2P DMA transfer?
>
> Yeah, see also the follow_pfn trickery in
> videobuf_dma_contig_user_get(), I think this is fully intentional and
> userspace abi we can't break :-/
We don't need to break uABI, it just needs to work properly in the
kernel:
vma = find_vma_intersection()
dma_buf = dma_buf_get_from_vma(vma)
sg = dma_buf_p2p_dma_map(dma_buf)
[.. do dma ..]
dma_buf_unmap(sg)
dma_buf_put(dma_buf)
It is as we discussed before, dma buf needs to be discoverable from a
VMA, at least for users doing this kind of stuff.
> Yup this should be done with dma_buf instead, and v4l has that. But
> old uapi and all that. This is why I said we might need a new
> VM_DYNAMIC_PFNMAP or so, to make follow_pfn not resolve this in the
> case where the driver manages the underlying iomem range (or whatever
> it is) dynamically and moves buffer objects around, like drm drivers
> do. But I looked, and we've run out of vma->vm_flags :-(
A VM flag doesn't help - we need to introduce some kind of lifetime,
and that has to be derived from the VMA. It needs data not just a flag
> The other problem is that I also have no real working clue about all
> the VM_* flags and what they all mean, and whether drm drivers set the
> right ones in all cases (they probably don't, but oh well).
> Documentation for this stuff in headers is a bit thin at times.
Yah, I don't really know either :\
The comment above vm_normal_page() is a bit helpful. Don't know what
VM_IO/VM_PFNMAP mean in their 3 combinations
There are very few places that set VM_PFNMAP without VM_IO..
Jason
next prev parent reply other threads:[~2020-10-04 12:51 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 17:53 [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Daniel Vetter
2020-10-02 17:53 ` [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Daniel Vetter
2020-10-02 18:06 ` Jason Gunthorpe
2020-10-02 18:16 ` Daniel Vetter
2020-10-02 23:31 ` Jason Gunthorpe
2020-10-03 8:34 ` Oded Gabbay
2020-10-03 9:40 ` Daniel Vetter
2020-10-04 12:50 ` Jason Gunthorpe [this message]
2020-10-04 16:09 ` Daniel Vetter
2020-10-05 17:28 ` Jason Gunthorpe
2020-10-05 18:16 ` Daniel Vetter
2020-10-05 18:37 ` Jason Gunthorpe
2020-10-05 18:54 ` Daniel Vetter
2020-10-05 22:43 ` Daniel Vetter
2020-10-05 23:41 ` Jason Gunthorpe
2020-10-06 6:23 ` Daniel Vetter
2020-10-06 12:26 ` Jason Gunthorpe
2020-10-06 13:08 ` Daniel Vetter
2020-10-07 10:47 ` Marek Szyprowski
2020-10-07 12:01 ` Daniel Vetter
2020-10-07 12:33 ` Marek Szyprowski
2020-10-07 12:44 ` Jason Gunthorpe
2020-10-07 12:47 ` Tomasz Figa
2020-10-07 12:58 ` Daniel Vetter
2020-10-07 13:06 ` Jason Gunthorpe
2020-10-07 13:34 ` Tomasz Figa
2020-10-07 13:42 ` Jason Gunthorpe
2020-10-07 14:08 ` Daniel Vetter
2020-10-07 14:11 ` Tomasz Figa
2020-10-07 14:22 ` Daniel Vetter
2020-10-07 15:05 ` Tomasz Figa
2020-10-07 14:58 ` Jason Gunthorpe
2020-10-07 13:06 ` Tomasz Figa
2020-10-07 13:14 ` Jason Gunthorpe
2020-10-05 15:03 ` Jan Kara
2020-10-02 22:39 ` John Hubbard
2020-10-03 9:45 ` Daniel Vetter
2020-10-03 22:52 ` John Hubbard
2020-10-03 23:24 ` Jason Gunthorpe
2020-10-04 11:20 ` Daniel Vetter
2020-10-05 17:35 ` Jason Gunthorpe
2020-10-02 18:22 ` [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Tomasz Figa
2020-10-02 19:21 ` Oded Gabbay
2020-10-05 17:38 [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Jason Gunthorpe
2020-10-05 17:47 ` Jason Gunthorpe
2020-10-06 3:36 ` Andrew Morton
2020-10-06 11:57 ` Jason Gunthorpe
2020-10-05 17:53 ` Jan Kara
2020-10-05 17:57 ` Jason Gunthorpe
2020-10-05 18:16 ` Daniel Vetter
2020-10-06 11:56 ` Daniel Vetter
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