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From: Marek Szyprowski <m.szyprowski@samsung.com>
To: dri-devel@lists.freedesktop.org,
	iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org,
	linux-kernel@vger.kernel.org
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@lst.de>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v7 00/36] DRM: fix struct sg_table nents vs. orig_nents misuse
Date: Tue, 30 Jun 2020 10:49:42 +0200	[thread overview]
Message-ID: <10cb27c9-286a-5ee5-dab1-183939e5b12d@samsung.com> (raw)
In-Reply-To: <20200619103636.11974-1-m.szyprowski@samsung.com>

Hi All,

On 19.06.2020 12:36, Marek Szyprowski wrote:
> During the Exynos DRM GEM rework and fixing the issues in the.
> drm_prime_sg_to_page_addr_arrays() function [1] I've noticed that most
> drivers in DRM framework incorrectly use nents and orig_nents entries of
> the struct sg_table.
>
> In case of the most DMA-mapping implementations exchanging those two
> entries or using nents for all loops on the scatterlist is harmless,
> because they both have the same value. There exists however a DMA-mapping
> implementations, for which such incorrect usage breaks things. The nents
> returned by dma_map_sg() might be lower than the nents passed as its
> parameter and this is perfectly fine. DMA framework or IOMMU is allowed
> to join consecutive chunks while mapping if such operation is supported
> by the underlying HW (bus, bridge, IOMMU, etc). Example of the case
> where dma_map_sg() might return 1 'DMA' chunk for the 4 'physical' pages
> is described here [2]
>
> The DMA-mapping framework documentation [3] states that dma_map_sg()
> returns the numer of the created entries in the DMA address space.
> However the subsequent calls to dma_sync_sg_for_{device,cpu} and
> dma_unmap_sg must be called with the original number of entries passed to
> dma_map_sg. The common pattern in DRM drivers were to assign the
> dma_map_sg() return value to sg_table->nents and use that value for
> the subsequent calls to dma_sync_sg_* or dma_unmap_sg functions. Also
> the code iterated over nents times to access the pages stored in the
> processed scatterlist, while it should use orig_nents as the numer of
> the page entries.
>
> I've tried to identify all such incorrect usage of sg_table->nents and
> this is a result of my research. It looks that the incorrect pattern has
> been copied over the many drivers mainly in the DRM subsystem. Too bad in
> most cases it even worked correctly if the system used a simple, linear
> DMA-mapping implementation, for which swapping nents and orig_nents
> doesn't make any difference. To avoid similar issues in the future, I've
> introduced a common wrappers for DMA-mapping calls, which operate directly
> on the sg_table objects. I've also added wrappers for iterating over the
> scatterlists stored in the sg_table objects and applied them where
> possible. This, together with some common DRM prime helpers, allowed me
> to almost get rid of all nents/orig_nents usage in the drivers. I hope
> that such change makes the code robust, easier to follow and copy/paste
> safe.
>
> The biggest TODO is DRM/i915 driver and I don't feel brave enough to fix
> it fully. The driver creatively uses sg_table->orig_nents to store the
> size of the allocate scatterlist and ignores the number of the entries
> returned by dma_map_sg function. In this patchset I only fixed the
> sg_table objects exported by dmabuf related functions. I hope that I
> didn't break anything there.
>
> Patches are based on top of Linux next-20200618. The required changes to
> DMA-mapping framework has been already merged to v5.8-rc1.
>
> If possible I would like ask for merging most of the patches via DRM
> tree.

David & Daniel: how would you like to merge those patches? They got 
quite a lot acks and some of them have dependencies on the DRM core. I 
would really like to get patches 1-28 merged via DRM (misc?) tree. Do 
you want me to prepare a branch and send a pull request?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


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      parent reply	other threads:[~2020-06-30  8:51 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200619103652eucas1p203d684adff0faa672ff5c8d383b52f23@eucas1p2.samsung.com>
2020-06-19 10:36 ` [PATCH v7 00/36] DRM: fix struct sg_table nents vs. orig_nents misuse Marek Szyprowski
     [not found]   ` <CGME20200619103653eucas1p2542a7f42db61b22a43919666368dbbfa@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 01/36] drm: prime: add common helper to check scatterlist contiguity Marek Szyprowski
2020-07-07 14:30       ` Andrzej Hajda
2020-07-07 15:03         ` Andrzej Hajda
     [not found]   ` <CGME20200619103654eucas1p227a1d6926d008ef21ba4e0b68a8de210@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 02/36] drm: prime: use sgtable iterators in drm_prime_sg_to_page_addr_arrays() Marek Szyprowski
2020-07-07 14:41       ` Andrzej Hajda
     [not found]   ` <CGME20200619103655eucas1p1b01cbe67526e2b2f8254eb20ccac1858@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 03/36] drm: core: fix common struct sg_table related issues Marek Szyprowski
2020-07-07 15:02       ` Andrzej Hajda
     [not found]   ` <CGME20200619103655eucas1p28ea4bf59428550217c8962666d6f077b@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 04/36] drm: amdgpu: " Marek Szyprowski
     [not found]       ` <bfbdf1ee-c970-d862-cc81-4712c34b7685@amd.com>
2020-07-07 13:06         ` Marek Szyprowski
     [not found]   ` <CGME20200619103656eucas1p262a08b701244745a547a0c38f26f83af@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 05/36] drm: armada: " Marek Szyprowski
     [not found]   ` <CGME20200619103657eucas1p2b7cec8f7b477c9574e2594ad6644a780@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 06/36] drm: etnaviv: " Marek Szyprowski
     [not found]   ` <CGME20200619103657eucas1p24bff92408adbd4715130fb47595a6187@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 07/36] drm: exynos: use common helper for a scatterlist contiguity check Marek Szyprowski
2020-07-07  9:35       ` Andrzej Hajda
2020-07-07 15:04         ` Andrzej Hajda
2020-07-14  0:28       ` Inki Dae
     [not found]   ` <CGME20200619103658eucas1p1c3236e2de2798c2d8c02279a9263e9a9@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 08/36] drm: exynos: fix common struct sg_table related issues Marek Szyprowski
2020-07-07  9:40       ` Andrzej Hajda
2020-07-07 15:05         ` Andrzej Hajda
2020-07-14  0:27       ` Inki Dae
     [not found]   ` <CGME20200619103659eucas1p27ece9865ea4cdd82d4ca4df06edef7e6@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 09/36] drm: i915: " Marek Szyprowski
     [not found]   ` <CGME20200619103659eucas1p15d57f701ea85df16e953bfd5098423f6@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 10/36] drm: lima: " Marek Szyprowski
     [not found]   ` <CGME20200619103700eucas1p13747c6a4d1a89f3cfc94a585ada9be4b@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 11/36] drm: mediatek: use common helper for a scatterlist contiguity check Marek Szyprowski
     [not found]   ` <CGME20200619103701eucas1p2323797b812f4d8c28e851aa80938a8dc@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 12/36] drm: mediatek: use common helper for extracting pages array Marek Szyprowski
     [not found]   ` <CGME20200619103702eucas1p1c57147013bbac3968f6ba073caec68b5@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 13/36] drm: msm: fix common struct sg_table related issues Marek Szyprowski
2020-06-19 14:45       ` Rob Clark
     [not found]   ` <CGME20200619103702eucas1p207b9cacc7460a334a0eda58c2b60a965@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 14/36] drm: omapdrm: use common helper for extracting pages array Marek Szyprowski
     [not found]   ` <CGME20200619103703eucas1p14faa1cec371efb0bf98ae696d58da64d@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 15/36] drm: omapdrm: fix common struct sg_table related issues Marek Szyprowski
     [not found]   ` <CGME20200619103703eucas1p2b8b0e90f9559c3fff12d61f76b861cc1@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 16/36] drm: panfrost: " Marek Szyprowski
     [not found]   ` <CGME20200619103704eucas1p1bf233e8914507323499186d9ab742c09@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 17/36] drm: radeon: " Marek Szyprowski
     [not found]   ` <CGME20200619103705eucas1p2d81a91b989d5aed5c7da6897173905cd@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 18/36] drm: rockchip: use common helper for a scatterlist contiguity check Marek Szyprowski
     [not found]   ` <CGME20200619103706eucas1p24f226bc00559f0812bc44d7933acd1e4@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 19/36] drm: rockchip: fix common struct sg_table related issues Marek Szyprowski
     [not found]   ` <CGME20200619103706eucas1p2b9a9926941e812db1111ec46a97695cd@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 20/36] drm: tegra: " Marek Szyprowski
     [not found]   ` <CGME20200619103707eucas1p1cdb34a10d5657bdd62fdf51fb7bf0146@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 21/36] drm: v3d: " Marek Szyprowski
     [not found]   ` <CGME20200619103708eucas1p2207ebc9373b820797675b91060a2a597@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 22/36] drm: virtio: " Marek Szyprowski
     [not found]   ` <CGME20200619103708eucas1p230ca99e915e759bc0e93cd844c91b311@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 23/36] drm: vmwgfx: " Marek Szyprowski
     [not found]   ` <CGME20200619103709eucas1p12c32fa6377caf78e5dc28ce0ff51e7a0@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 24/36] drm: xen: " Marek Szyprowski
     [not found]   ` <CGME20200619103710eucas1p1873c8ebb37e6717a5864c31d10b50efd@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 25/36] xen: gntdev: " Marek Szyprowski
     [not found]   ` <CGME20200619103710eucas1p1160d521b10c9afdb8e447e261072bfd4@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 26/36] drm: host1x: " Marek Szyprowski
     [not found]   ` <CGME20200619103711eucas1p188e07cb9aaad13d39238aac4fe84b10c@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 27/36] drm: rcar-du: " Marek Szyprowski
     [not found]   ` <CGME20200619103712eucas1p1a29d1fe41061ed5b138a9cdd5d811419@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 28/36] dmabuf: " Marek Szyprowski
     [not found]   ` <CGME20200619103713eucas1p2f4b6b66a376a72d1bf62ea6d92572045@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 29/36] staging: ion: remove dead code Marek Szyprowski
     [not found]   ` <CGME20200619103714eucas1p2bfc6c1d97d7913ad5988e3aaef8cc5ff@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 30/36] staging: ion: fix common struct sg_table related issues Marek Szyprowski
     [not found]   ` <CGME20200619103714eucas1p18db6efd1a380fc0bdb16174ee85036fa@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 31/36] staging: tegra-vde: " Marek Szyprowski
     [not found]       ` <20200621070015.0cf833ab@dimatab>
2020-06-30 10:07         ` Marek Szyprowski
2020-07-01  1:45           ` Dmitry Osipenko
     [not found]   ` <CGME20200619103715eucas1p12d01355499fbecb8632472b1b8230e6f@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 32/36] misc: fastrpc: " Marek Szyprowski
     [not found]   ` <CGME20200619103716eucas1p1b7c50f7b421fb29829050b9355e3e644@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 33/36] rapidio: " Marek Szyprowski
     [not found]       ` <CGME20200630084445eucas1p1e85857b5d046648578f1447f8ba521a5@eucas1p1.samsung.com>
2020-06-30  8:44         ` [PATCH v8] " Marek Szyprowski
     [not found]   ` <CGME20200619103716eucas1p28d6da172346acf044d3c1f213d9543ef@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 34/36] samples: vfio-mdev/mbochs: " Marek Szyprowski
     [not found]   ` <CGME20200619103717eucas1p23b82366794c92cc70c0492e4ca29c4a1@eucas1p2.samsung.com>
2020-06-19 10:36     ` [PATCH v7 35/36] media: pci: fix common ALSA DMA-mapping related codes Marek Szyprowski
     [not found]   ` <CGME20200619103718eucas1p11cd577b435672197f48bfcba2d06bc18@eucas1p1.samsung.com>
2020-06-19 10:36     ` [PATCH v7 36/36] videobuf2: use sgtable-based scatterlist wrappers Marek Szyprowski
     [not found]       ` <CGME20200630104527eucas1p13f19c24ff053556fb1fa7dc72be14c77@eucas1p1.samsung.com>
2020-06-30 10:45         ` [PATCH v8] " Marek Szyprowski
2020-06-30  8:49   ` Marek Szyprowski [this message]

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