udmabuf: Do not create malformed scatterlists

[ Upstream commit 5bf888673e ]

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: 0c8b91ef51 ("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: 504e2b4ab9 ("dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/dma-buf/udmabuf.c

@@ -100,14 +100,16 @@ 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);
 }