From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
Jan Kara <jack@suse.cz>, Pawel Osciak <pawel@osciak.com>,
KVM list <kvm@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
John Hubbard <jhubbard@nvidia.com>,
LKML <linux-kernel@vger.kernel.org>,
DRI Development <dri-devel@lists.freedesktop.org>,
Tomasz Figa <tfiga@chromium.org>, Jason Gunthorpe <jgg@ziepe.ca>,
J??r??me Glisse <jglisse@redhat.com>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
Daniel Vetter <daniel.vetter@intel.com>,
Kyungmin Park <kyungmin.park@samsung.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
Date: Wed, 4 Nov 2020 17:26:58 +0100 [thread overview]
Message-ID: <CAKMK7uH=0+3FSR4LxP7bJUB4BsCcnCzfK2=D+2Am9QNmfZEmfw@mail.gmail.com> (raw)
In-Reply-To: <20201104162125.GA13007@infradead.org>
On Wed, Nov 4, 2020 at 5:21 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Wed, Nov 04, 2020 at 04:54:19PM +0100, Daniel Vetter wrote:
> > I don't really have a box here, but dma_mmap_attrs() and friends to
> > mmap dma_alloc_coherent memory is set up as VM_IO | VM_PFNMAP (it's
> > actually enforced since underneath it uses remap_pfn_range), and
> > usually (except if it's pre-cma carveout) that's just normal struct
> > page backed memory. Sometimes from a cma region (so will be caught by
> > the cma page check), but if you have an iommu to make it
> > device-contiguous, that's not needed.
>
> dma_mmap_* memory may or may not be page backed, but it absolutely
> must not be resolved by get_user_pages and friends as it is special.
> So yes, not being able to get a struct page back from such an mmap is
> a feature.
Yes, that's clear.
What we're discussing is whether gup_fast and pup_fast also obey this,
or fall over and can give you the struct page that's backing the
dma_mmap_* memory. Since the _fast variant doesn't check for
vma->vm_flags, and afaict that's the only thing which closes this gap.
And like you restate, that would be a bit a problem. So where's that
check which Jason&me aren't spotting?
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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next prev parent reply other threads:[~2020-11-04 16:27 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-30 10:08 [PATCH v5 00/15] follow_pfn and other iomap races Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 01/15] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 02/15] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 03/15] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 04/15] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-30 14:11 ` Tomasz Figa
2020-10-30 14:37 ` Daniel Vetter
2020-11-02 18:19 ` Tomasz Figa
2020-10-31 2:55 ` John Hubbard
2020-10-31 14:45 ` Daniel Vetter
2020-11-01 5:22 ` John Hubbard
2020-11-01 10:30 ` Daniel Vetter
2020-11-01 21:13 ` John Hubbard
2020-11-01 22:50 ` Daniel Vetter
2020-11-04 14:00 ` Jason Gunthorpe
2020-11-04 15:54 ` Daniel Vetter
[not found] ` <20201104162125.GA13007@infradead.org>
2020-11-04 16:26 ` Daniel Vetter [this message]
[not found] ` <20201104163758.GA17425@infradead.org>
[not found] ` <20201104164119.GA18218@infradead.org>
2020-11-04 18:17 ` Jason Gunthorpe
2020-11-04 18:44 ` John Hubbard
2020-11-04 19:02 ` Jason Gunthorpe
2020-11-05 9:25 ` Daniel Vetter
2020-11-05 12:49 ` Jason Gunthorpe
2020-11-06 4:08 ` John Hubbard
2020-11-06 10:01 ` Daniel Vetter
2020-11-06 10:27 ` Daniel Vetter
2020-11-06 12:55 ` Jason Gunthorpe
2020-11-09 8:44 ` Thomas Hellström
2020-11-09 20:19 ` Jason Gunthorpe
2020-11-06 12:58 ` Jason Gunthorpe
2020-10-30 10:08 ` [PATCH v5 06/15] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 07/15] mm: Close race in generic_access_phys Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 08/15] mm: Add unsafe_follow_pfn Daniel Vetter
[not found] ` <20201102072931.GA16419@infradead.org>
2020-11-02 12:56 ` Daniel Vetter
2020-11-02 13:01 ` Jason Gunthorpe
2020-11-02 13:23 ` Daniel Vetter
2020-11-02 15:52 ` Jason Gunthorpe
2020-11-02 16:42 ` Daniel Vetter
2020-11-02 17:16 ` Jason Gunthorpe
2020-10-30 10:08 ` [PATCH v5 09/15] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 10/15] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 11/15] PCI: Obey iomem restrictions for procfs mmap Daniel Vetter
2020-11-03 21:28 ` Bjorn Helgaas
2020-11-03 22:09 ` Dan Williams
2020-11-04 8:44 ` Daniel Vetter
2020-11-04 16:50 ` Bjorn Helgaas
2020-11-04 20:12 ` Dan Williams
2020-11-05 9:34 ` Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 12/15] /dev/mem: Only set filp->f_mapping Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 13/15] resource: Move devmem revoke code to resource framework Daniel Vetter
2020-10-31 6:36 ` John Hubbard
2020-10-31 14:40 ` Daniel Vetter
2020-11-03 6:06 ` [resource] 22b17dc667: Kernel panic - not syncing: Fatal exception lkp
2020-11-03 6:15 ` John Hubbard
2020-11-03 10:10 ` Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 14/15] sysfs: Support zapping of binary attr mmaps Daniel Vetter
2020-10-30 10:08 ` [PATCH v5 15/15] PCI: Revoke mappings like devmem Daniel Vetter
2020-10-30 19:22 ` Dan Williams
2020-11-03 21:30 ` Bjorn Helgaas
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