intel-iommu: Check for identity mapping candidate using system dma mask

The identity mapping code appears to make the assumption that if the
devices dma_mask is greater than 32bits the device can use identity
mapping.  But that is not true: take the case where we have a 40bit
device in a 44bit architecture. The device can potentially receive a
physical address that it will truncate and cause incorrect addresses
to be used.

Instead check to see if the device's dma_mask is large enough
to address the system's dma_mask.

Signed-off-by: Mike Travis <travis@sgi.com>
Reviewed-by: Mike Habeck <habeck@sgi.com>
Cc: stable@kernel.org
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 4eaec2fa1369..dcf051d53b74 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -2316,8 +2316,19 @@ static int iommu_should_identity_map(struct pci_dev *pdev, int startup)
          * Assume that they will -- if they turn out not to be, then we can 
          * take them out of the 1:1 domain later.
          */
-        if (!startup)
-                return pdev->dma_mask > DMA_BIT_MASK(32);
+        if (!startup) {
+                /*
+                 * If the device's dma_mask is less than the system's memory
+                 * size then this is not a candidate for identity mapping.
+                 */
+                u64 dma_mask = pdev->dma_mask;
+
+                if (pdev->dev.coherent_dma_mask &&
+                    pdev->dev.coherent_dma_mask < dma_mask)
+                        dma_mask = pdev->dev.coherent_dma_mask;
+
+                return dma_mask >= dma_get_required_mask(&pdev->dev);
+        }
 
         return 1;
 }