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61 lines
2.2 KiB
Diff
61 lines
2.2 KiB
Diff
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From 153f1e1def226f87cc4c307d2806b000a820f64b Mon Sep 17 00:00:00 2001
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From: Gurchetan Singh <gurchetansingh@chromium.org>
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Date: Tue, 17 Dec 2019 15:02:28 -0800
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Subject: [PATCH] udmabuf: fix dma-buf cpu access
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Commit 1ffe09590121fbb3786d6c860acdd200f7ab095c upstream.
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I'm just going to put Chia's review comment here since it sums
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the issue rather nicely:
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"(1) Semantically, a dma-buf is in DMA domain. CPU access from the
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importer must be surrounded by {begin,end}_cpu_access. This gives the
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exporter a chance to move the buffer to the CPU domain temporarily.
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(2) When the exporter itself has other means to do CPU access, it is
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only reasonable for the exporter to move the buffer to the CPU domain
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before access, and to the DMA domain after access. The exporter can
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potentially reuse {begin,end}_cpu_access for that purpose.
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Because of (1), udmabuf does need to implement the
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{begin,end}_cpu_access hooks. But "begin" should mean
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dma_sync_sg_for_cpu and "end" should mean dma_sync_sg_for_device.
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Because of (2), if userspace wants to continuing accessing through the
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memfd mapping, it should call udmabuf's {begin,end}_cpu_access to
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avoid cache issues."
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Reported-by: Chia-I Wu <olvaffe@gmail.com>
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Suggested-by: Chia-I Wu <olvaffe@gmail.com>
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Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks")
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Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
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Link: http://patchwork.freedesktop.org/patch/msgid/20191217230228.453-1-gurchetansingh@chromium.org
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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---
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drivers/dma-buf/udmabuf.c | 7 +++----
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1 file changed, 3 insertions(+), 4 deletions(-)
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--- a/drivers/dma-buf/udmabuf.c
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+++ b/drivers/dma-buf/udmabuf.c
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@@ -122,9 +122,8 @@ static int begin_cpu_udmabuf(struct dma_
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if (IS_ERR(ubuf->sg))
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return PTR_ERR(ubuf->sg);
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} else {
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- dma_sync_sg_for_device(dev, ubuf->sg->sgl,
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- ubuf->sg->nents,
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- direction);
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+ dma_sync_sg_for_cpu(dev, ubuf->sg->sgl, ubuf->sg->nents,
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+ direction);
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}
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return 0;
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@@ -139,7 +138,7 @@ static int end_cpu_udmabuf(struct dma_bu
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if (!ubuf->sg)
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return -EINVAL;
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- dma_sync_sg_for_cpu(dev, ubuf->sg->sgl, ubuf->sg->nents, direction);
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+ dma_sync_sg_for_device(dev, ubuf->sg->sgl, ubuf->sg->nents, direction);
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return 0;
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}
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