[PATCH v2 0/3] xen/swiotlb: fix an issue and improve swiotlb-xen

[PATCH v2 0/3] xen/swiotlb: fix an issue and improve swiotlb-xen

[Juergen Gross]

While hunting an issue in swiotlb-xen I stumbled over a wrong test
and found some areas for improvement.

Juergen Gross (3):
  xen/swiotlb: fix condition for calling xen_destroy_contiguous_region()
  xen/swiotlb: simplify range_straddles_page_boundary()
  xen/swiotlb: remember having called xen_create_contiguous_region()

 drivers/xen/swiotlb-xen.c  | 36 ++++++++++++------------------------
 include/linux/page-flags.h |  3 +++
 2 files changed, 15 insertions(+), 24 deletions(-)

-- 
2.16.4

[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@vger.kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
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

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

[Jan Beulich]

>>> On 29.05.19 at 11:04, <jgross@suse.com> wrote:
> 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@vger.kernel.org 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>