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authorGurchetan Singh <gurchetansingh@chromium.org>2019-12-17 15:02:28 -0800
committerGerd Hoffmann <kraxel@redhat.com>2019-12-18 09:11:38 +0100
commit1ffe09590121fbb3786d6c860acdd200f7ab095c (patch)
treec303a11635d34db2d5359c9d0d7ac1dd94f15f40 /drivers/dma-buf
parentc8d4a56082eebabbf96ddb86238808c30124f06b (diff)
downloadlinux-1ffe09590121fbb3786d6c860acdd200f7ab095c.tar.bz2
udmabuf: fix dma-buf cpu access
I'm just going to put Chia's review comment here since it sums the issue rather nicely: "(1) Semantically, a dma-buf is in DMA domain. CPU access from the importer must be surrounded by {begin,end}_cpu_access. This gives the exporter a chance to move the buffer to the CPU domain temporarily. (2) When the exporter itself has other means to do CPU access, it is only reasonable for the exporter to move the buffer to the CPU domain before access, and to the DMA domain after access. The exporter can potentially reuse {begin,end}_cpu_access for that purpose. Because of (1), udmabuf does need to implement the {begin,end}_cpu_access hooks. But "begin" should mean dma_sync_sg_for_cpu and "end" should mean dma_sync_sg_for_device. Because of (2), if userspace wants to continuing accessing through the memfd mapping, it should call udmabuf's {begin,end}_cpu_access to avoid cache issues." Reported-by: Chia-I Wu <olvaffe@gmail.com> Suggested-by: Chia-I Wu <olvaffe@gmail.com> Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks") Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org> Link: http://patchwork.freedesktop.org/patch/msgid/20191217230228.453-1-gurchetansingh@chromium.org Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Diffstat (limited to 'drivers/dma-buf')
-rw-r--r--drivers/dma-buf/udmabuf.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 61b0a2cff874..acb26c627d27 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -122,9 +122,8 @@ static int begin_cpu_udmabuf(struct dma_buf *buf,
if (IS_ERR(ubuf->sg))
return PTR_ERR(ubuf->sg);
} else {
- dma_sync_sg_for_device(dev, ubuf->sg->sgl,
- ubuf->sg->nents,
- direction);
+ dma_sync_sg_for_cpu(dev, ubuf->sg->sgl, ubuf->sg->nents,
+ direction);
}
return 0;
@@ -139,7 +138,7 @@ static int end_cpu_udmabuf(struct dma_buf *buf,
if (!ubuf->sg)
return -EINVAL;
- dma_sync_sg_for_cpu(dev, ubuf->sg->sgl, ubuf->sg->nents, direction);
+ dma_sync_sg_for_device(dev, ubuf->sg->sgl, ubuf->sg->nents, direction);
return 0;
}