[PATCH 6.6.y 1/2] udmabuf: Do not create malformed scatterlists

[Sasha Levin <sashal@kernel.org>]

From: Jason Gunthorpe <jgg@nvidia.com>

[ Upstream commit 5bf888673e0dda5a53220fa0c4956271a46c353c ]

Using a sg_set_folio() loop for every 4K results in a malformed scatterlist
because sg_set_folio() has an issue with offsets > PAGE_SIZE and because
scatterlist expects the creator to build a list which consolidates any
physical contiguity.

sg_alloc_table_from_pages() creates a valid scatterlist directly from a
struct page array, so go back to that.

Remove the offsets allocation and just store an array of tail pages as it
did before the below commit. Everything wants that anyhow.

Fixes: 0c8b91ef5100 ("udmabuf: add back support for mapping hugetlb pages")
Reported-by: Julian Orth <ju.orth@gmail.com>
Closes: https://lore.kernel.org/all/20260308-scatterlist-v1-1-39c4566b0bba@gmail.com/
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Link: https://patch.msgid.link/0-v1-42779f29381a+4b9-udmabuf_sg_jgg@nvidia.com
Stable-dep-of: 504e2b4ab97a ("dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/dma-buf/udmabuf.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 980975ffc55d3c..de3a7e395a6d99 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -99,14 +99,16 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
 					0, ubuf->pagecount << PAGE_SHIFT,
 					GFP_KERNEL);
 	if (ret < 0)
-		goto err;
+		goto err_alloc;
+
 	ret = dma_map_sgtable(dev, sg, direction, 0);
 	if (ret < 0)
-		goto err;
+		goto err_map;
 	return sg;
 
-err:
+err_map:
 	sg_free_table(sg);
+err_alloc:
 	kfree(sg);
 	return ERR_PTR(ret);
 }
-- 
2.53.0