From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: "Jason Gunthorpe" <jgg@ziepe.ca>,
"Mauro Carvalho Chehab" <mchehab+huawei@kernel.org>,
linux-s390 <linux-s390@vger.kernel.org>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
"Jan Kara" <jack@suse.cz>, "Kees Cook" <keescook@chromium.org>,
"KVM list" <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"DRI Development" <dri-devel@lists.freedesktop.org>,
"Linux MM" <linux-mm@kvack.org>,
"Jérôme Glisse" <jglisse@redhat.com>,
"John Hubbard" <jhubbard@nvidia.com>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>
Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn
Date: Mon, 12 Oct 2020 15:49:07 +0200 [thread overview]
Message-ID: <CAKMK7uGLOubJrr9A=usxkoVx+nXDW3bxhykfeU-TYXTUZyBoeQ@mail.gmail.com> (raw)
In-Reply-To: <ed68968b-27bc-d776-8da8-ef21d6b3c378@samsung.com>
On Mon, Oct 12, 2020 at 12:47 PM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi Jason,
>
> On 09.10.2020 14:48, Jason Gunthorpe wrote:
> > On Fri, Oct 09, 2020 at 02:37:23PM +0200, Mauro Carvalho Chehab wrote:
> >
> >> I'm not a mm/ expert, but, from what I understood from Daniel's patch
> >> description is that this is unsafe *only if* __GFP_MOVABLE is used.
> > No, it is unconditionally unsafe. The CMA movable mappings are
> > specific VMAs that will have bad issues here, but there are other
> > types too.
>
> I'm trying to follow this thread, but I really wonder what do you mean
> by CMA movable mappings? If a buffer has been allocated from CMA and
> used for DMA, it won't be moved in the memory. It will stay at the same
> physical memory address all the time until freed by the owner. It just a
> matter of proper usage count tracking to delay freeing if it is still
> used somewhere.
Yup. The problem is that this usage count tracking doesn't exist. And
drivers could at least in theory treat CMA like vram and swap buffers
in&out of it, so just refcounting the userspace vma isn't enough. In
practice, right now, it might be enough for CMA drivers though (but
there's more that's possible here).
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2020-10-12 13:49 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
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 [this message]
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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