[PATCH 3.16 104/305] xen-swiotlb: use actually allocated size on check physical continuous

[Ben Hutchings]

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Jin <joe.jin@xxxxxxxxxx>

commit 7250f422da0480d8512b756640f131b9b893ccda upstream.

xen_swiotlb_{alloc,free}_coherent() allocate/free memory based on the
order of the pages and not size argument (bytes). This is inconsistent with
range_straddles_page_boundary and memset which use the 'size' value,
which may lead to not exchanging memory with Xen (range_straddles_page_boundary()
returned true). And then the call to xen_swiotlb_free_coherent() would
actually try to exchange the memory with Xen, leading to the kernel
hitting an BUG (as the hypercall returned an error).

This patch fixes it by making the 'size' variable be of the same size
as the amount of memory allocated.

Signed-off-by: Joe Jin <joe.jin@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Christoph Helwig <hch@xxxxxx>
Cc: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Cc: John Sobecki <john.sobecki@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
[bwh: Backported to 3.16:
 - Use PAGE_SHIFT instead of XEN_PAGE_SHIFT
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/xen/swiotlb-xen.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -311,6 +311,9 @@ xen_swiotlb_alloc_coherent(struct device
 	*/
 	flags &= ~(__GFP_DMA | __GFP_HIGHMEM);
 
+	/* Convert the size to actually allocated. */
+	size = 1UL << (order + PAGE_SHIFT);
+
 	if (dma_alloc_from_coherent(hwdev, size, dma_handle, &ret))
 		return ret;
 
@@ -366,6 +369,9 @@ xen_swiotlb_free_coherent(struct device
 	 * physical address */
 	phys = xen_bus_to_phys(dev_addr);
 
+	/* Convert the size to actually allocated. */
+	size = 1UL << (order + PAGE_SHIFT);
+
 	if (((dev_addr + size - 1 <= dma_mask)) ||
 	    range_straddles_page_boundary(phys, size))
 		xen_destroy_contiguous_region(phys, order);