From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: "Jason Gunthorpe" <jgg@ziepe.ca>,
"DRI Development" <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
"KVM list" <kvm@vger.kernel.org>, "Linux MM" <linux-mm@kvack.org>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
linux-s390 <linux-s390@vger.kernel.org>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Kees Cook" <keescook@chromium.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"John Hubbard" <jhubbard@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Linus Torvalds" <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn
Date: Sat, 10 Oct 2020 13:56:00 +0200 [thread overview]
Message-ID: <CAKMK7uEwT0TBvHtVMHeSW2gwt2nhm7mpd2pNuUHUCz=EaYM3yw@mail.gmail.com> (raw)
In-Reply-To: <20201010133929.746d0529@coco.lan>
On Sat, Oct 10, 2020 at 1:39 PM Mauro Carvalho Chehab
<mchehab+huawei@kernel.org> wrote:
>
> Em Sat, 10 Oct 2020 12:53:49 +0200
> Daniel Vetter <daniel.vetter@ffwll.ch> escreveu:
>
> > Hi Mauro,
> >
> > You might want to read the patches more carefully, because what you're
> > demanding is what my patches do. Short summary:
> >
> > - if STRICT_FOLLOW_PFN is set:
> > a) normal memory is handled as-is (i.e. your example works) through
> > the addition of FOLL_LONGTERM. This is the "pin the pages correctly"
> > approach you're demanding
> > b) for non-page memory (zerocopy sharing before dma-buf was upstreamed
> > is the only use-case for this) it is correctly rejected with -EINVAL
> >
> > - if you do have blobby userspace which requires the zero-copy using
> > userptr to work, and doesn't have any of the fallbacks implemented
> > that you describe, this would be a regression. That's why
> > STRICT_FOLLOW_PFN can be unset. And yes there's a real security issue
> > in this usage, Marek also confirmed that the removal of the vma copy
> > code a few years ago essentially broke even the weak assumptions that
> > made the code work 10+ years ago when it was merged.
> >
> > so tdlr; Everything you described will keep working even with the new
> > flag set, and everything you demand must be implemented _is_
> > implemented in this patch series.
> >
> > Also please keep in mind that we are _not_ talking about the general
> > userptr support that was merge ~20 years ago. This patch series here
> > is _only_ about the zerocpy userptr support merged with 50ac952d2263
> > ("[media] videobuf2-dma-sg: Support io userptr operations on io
> > memory") in 2013.
>
> Ok, now it is making more sense. Please update the comments for
> patch 10/17 to describe the above.
Will do.
> We need some time to test this though, in order to check if no
> regressions were added (except the ones due to changeset 50ac952d2263).
Yeah testing of the previous patches to switch to FOLL_LONGTERM would
be really good. I also need that for habanalabs and ideally exynos
too. All the userptr for normal memory should keep working, and with
FOLL_LONGTERM it should actually work better, since with that it
should now correctly interact with pagecache and fs code, not just
with anon memory from malloc.
Thanks, Daniel
> > Why this hack was merged in 2013 when we merged dma-buf almost 2 years
> > before that I have no idea about. Imo that patch simply should never
> > have landed, and instead dma-buf support prioritized.
>
> If I recall correctly, we didn't have any DMABUF support
> at the media subsystem, back on 2013.
>
> It took some time for the DMA-BUF to arrive at media, as this
> was not a top priority. Also, there aren't many developers that
> understand the memory model well enough to implement DMA-BUF support
> and touch the VB2 code, which is quite complex, as it supports
> lots of different ways for I/O, plus works with vmalloc, DMA
> contig and DMA scatter/gather.
>
> Changes there should carefully be tested against different
> drivers, in order to avoid regressions on it.
>
> > Cheers, Daniel
>
> Thanks,
> Mauro
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2020-10-10 22:18 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 7:59 [PATCH v2 00/17] follow_pfn and other iomap races Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 01/17] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-16 7:42 ` John Hubbard
2020-10-09 7:59 ` [PATCH v2 02/17] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 03/17] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-10 20:26 ` Oded Gabbay
2020-10-10 21:32 ` Daniel Vetter
2020-10-10 21:41 ` Daniel Vetter
2020-10-10 21:47 ` Oded Gabbay
2020-10-16 7:45 ` John Hubbard
2020-10-09 7:59 ` [PATCH v2 04/17] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 05/17] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-16 7:54 ` John Hubbard
2020-10-16 8:03 ` Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 06/17] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-09 10:14 ` Mauro Carvalho Chehab
2020-10-09 16:57 ` Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 07/17] mm: Close race in generic_access_phys Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 08/17] s390/pci: Remove races against pte updates Daniel Vetter
2020-10-12 14:03 ` Niklas Schnelle
2020-10-12 14:19 ` Daniel Vetter
2020-10-12 14:39 ` Niklas Schnelle
2020-10-21 7:55 ` Niklas Schnelle
2020-10-22 7:39 ` Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 09/17] mm: Add unsafe_follow_pfn Daniel Vetter
2020-10-09 10:34 ` Mauro Carvalho Chehab
2020-10-09 12:21 ` Jason Gunthorpe
2020-10-09 12:37 ` Mauro Carvalho Chehab
2020-10-09 12:39 ` Mauro Carvalho Chehab
2020-10-09 12:48 ` Jason Gunthorpe
2020-10-09 17:52 ` Daniel Vetter
2020-10-09 18:01 ` Jason Gunthorpe
2020-10-09 19:31 ` Daniel Vetter
2020-10-10 9:21 ` Mauro Carvalho Chehab
2020-10-10 10:53 ` Daniel Vetter
2020-10-10 11:39 ` Mauro Carvalho Chehab
2020-10-10 11:56 ` Daniel Vetter [this message]
2020-10-10 17:22 ` Tomasz Figa
2020-10-10 21:35 ` Laurent Pinchart
2020-10-10 21:50 ` Daniel Vetter
2020-10-11 6:27 ` Mauro Carvalho Chehab
2020-10-11 6:36 ` Mauro Carvalho Chehab
2020-10-10 21:11 ` Laurent Pinchart
2020-10-12 10:46 ` Marek Szyprowski
2020-10-12 13:49 ` Daniel Vetter
2020-10-10 17:30 ` Tomasz Figa
2020-10-09 7:59 ` [PATCH v2 10/17] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-10 9:24 ` Mauro Carvalho Chehab
2020-10-09 7:59 ` [PATCH v2 11/17] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 12/17] PCI: Obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 13/17] /dev/mem: Only set filp->f_mapping Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 14/17] resource: Move devmem revoke code to resource framework Daniel Vetter
2020-10-09 10:59 ` Greg Kroah-Hartman
2020-10-09 12:31 ` Jason Gunthorpe
2020-10-09 14:24 ` Daniel Vetter
2020-10-09 14:32 ` Jason Gunthorpe
2020-10-09 18:28 ` Dan Williams
2020-10-15 0:09 ` Jason Gunthorpe
2020-10-15 7:52 ` Daniel Vetter
2020-10-15 7:55 ` Daniel Vetter
2020-10-15 15:29 ` Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 15/17] sysfs: Support zapping of binary attr mmaps Daniel Vetter
2020-10-09 10:58 ` Greg Kroah-Hartman
2020-10-09 7:59 ` [PATCH v2 16/17] PCI: Revoke mappings like devmem Daniel Vetter
2020-10-09 7:59 ` [PATCH v2 17/17] drm/i915: Properly request PCI BARs Daniel Vetter
2020-10-09 9:47 ` Ville Syrjälä
2020-10-09 10:01 ` Daniel Vetter
2020-10-09 10:41 ` Ville Syrjälä
2020-10-09 14:18 ` Daniel Vetter
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