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-rw-r--r--target/linux/bcm27xx/patches-5.4/950-0731-udmabuf-fix-dma-buf-cpu-access.patch60
1 files changed, 60 insertions, 0 deletions
diff --git a/target/linux/bcm27xx/patches-5.4/950-0731-udmabuf-fix-dma-buf-cpu-access.patch b/target/linux/bcm27xx/patches-5.4/950-0731-udmabuf-fix-dma-buf-cpu-access.patch
new file mode 100644
index 0000000000..14cfe8aed3
--- /dev/null
+++ b/target/linux/bcm27xx/patches-5.4/950-0731-udmabuf-fix-dma-buf-cpu-access.patch
@@ -0,0 +1,60 @@
+From 153f1e1def226f87cc4c307d2806b000a820f64b Mon Sep 17 00:00:00 2001
+From: Gurchetan Singh <gurchetansingh@chromium.org>
+Date: Tue, 17 Dec 2019 15:02:28 -0800
+Subject: [PATCH] udmabuf: fix dma-buf cpu access
+
+Commit 1ffe09590121fbb3786d6c860acdd200f7ab095c upstream.
+
+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>
+---
+ drivers/dma-buf/udmabuf.c | 7 +++----
+ 1 file changed, 3 insertions(+), 4 deletions(-)
+
+--- a/drivers/dma-buf/udmabuf.c
++++ b/drivers/dma-buf/udmabuf.c
+@@ -122,9 +122,8 @@ static int begin_cpu_udmabuf(struct dma_
+ 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_bu
+ 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;
+ }
+