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From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
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 13:39:29 +0200
Message-ID: <20201010133929.746d0529@coco.lan> (raw)
In-Reply-To: <CAKMK7uEKP5UMKeQHkTHWYUJkp=mz-Hvh-fJZy1KP3kT2xHpHrg@mail.gmail.com>

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.

We need some time to test this though, in order to check if no
regressions were added (except the ones due to changeset 50ac952d2263).

> 
> 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

  reply index

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 [this message]
2020-10-10 11:56                   ` Daniel Vetter
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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