[PATCH v2 1/3] xen/swiotlb: fix condition for calling xen_destroy_contiguous_region()

[Juergen Gross]

The condition in xen_swiotlb_free_coherent() for deciding whether to
call xen_destroy_contiguous_region() is wrong: in case the region to
be freed is not contiguous calling xen_destroy_contiguous_region() is
the wrong thing to do: it would result in inconsistent mappings of
multiple PFNs to the same MFN. This will lead to various strange
crashes or data corruption.

Instead of calling xen_destroy_contiguous_region() in that case a
warning should be issued as that situation should never occur.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
V2: always issue a warning in case xen_destroy_contiguous_region()
    isn't called (Jan Beulich)
---
 drivers/xen/swiotlb-xen.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 5dcb06fe9667..1caadca124b3 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -360,8 +360,8 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 	/* Convert the size to actually allocated. */
 	size = 1UL << (order + XEN_PAGE_SHIFT);
 
-	if (((dev_addr + size - 1 <= dma_mask)) ||
-	    range_straddles_page_boundary(phys, size))
+	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
+		     range_straddles_page_boundary(phys, size)))
 		xen_destroy_contiguous_region(phys, order);
 
 	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
-- 
2.16.4