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>,
Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
Daniel Vetter <daniel@ffwll.ch>,
xen-devel@lists.xenproject.org,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: [PATCH v5 39/38] drm: xen: fix common struct sg_table related issues
Date: Fri, 22 May 2020 14:56:52 +0200 [thread overview]
Message-ID: <20200522125652.18435-1-m.szyprowski@samsung.com> (raw)
In-Reply-To: <20200513132114.6046-1-m.szyprowski@samsung.com>
The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().
struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).
It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.
Fix the code to refer to proper nents or orig_nents entries. This driver
reports the number of the pages in the imported scatterlist, so it should
refer to sg_table->orig_nents entry.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/
This patch has been resurrected on Oleksandr Andrushchenko request. The
patch was a part of v2 patchset, but then I've dropped it as it only
fixes the debug output, thus I didn't consider it so critical.
---
drivers/gpu/drm/xen/xen_drm_front_gem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
index f0b85e0..ba4bdc5 100644
--- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
+++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
@@ -215,7 +215,7 @@ struct drm_gem_object *
return ERR_PTR(ret);
DRM_DEBUG("Imported buffer of size %zu with nents %u\n",
- size, sgt->nents);
+ size, sgt->orig_nents);
return &xen_obj->base;
}
--
1.9.1
prev parent reply other threads:[~2020-05-22 12:57 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200513132114.6046-1-m.szyprowski@samsung.com>
[not found] ` <20200513133245.6408-1-m.szyprowski@samsung.com>
[not found] ` <CGME20200513133316eucas1p2ad01d27ea4388cb50424bcf112d710ef@eucas1p2.samsung.com>
2020-05-13 13:32 ` [PATCH v5 27/38] xen: gntdev: fix common struct sg_table related issues Marek Szyprowski
2020-05-18 5:17 ` Jürgen Groß
[not found] ` <CGME20200522125708eucas1p233b80b0741f087a84d47f24b6d91985f@eucas1p2.samsung.com>
2020-05-22 12:56 ` Marek Szyprowski [this message]
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