[PATCH 3/4 v2] intel-iommu: don't cache iova above 32bit cachingboundary

[Chris Wright]

Mike Travis and Mike Habeck reported an issue where iova allocation
would return a range that was larger than a device's dma mask.

https://lkml.org/lkml/2011/3/29/423

The dmar initialization code will reserve all PCI MMIO regions and copy
those reservations into a domain specific iova tree.  It is possible for
one of those regions to be above the dma mask of a device.  It is typical
to allocate iovas with a 32bit mask (despite device's dma mask possibly
being larger) and cache the result until it exhausts the lower 32bit
address space.  Freeing the iova range that is >= the last iova in the
lower 32bit range when there is still an iova above the 32bit range will
corrupt the cached iova by pointing it to a region that is above 32bit.
If that region is also larger than the device's dma mask, a subsequent
allocation will return an unusable iova and cause dma failure.

Simply don't cache an iova that is above the 32bit caching boundary.

Reported-by: Mike Travis <travis@xxxxxxx>
Reported-by: Mike Habeck <habeck@xxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx 
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
Mike or Mike, can you try this?  I was able to reproduce the failure
in a few different ways and successfully test this patch against those
failures, but w/out real hw.

 drivers/pci/iova.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/iova.c b/drivers/pci/iova.c
index 7914951..1690ca4 100644
--- a/drivers/pci/iova.c
+++ b/drivers/pci/iova.c
@@ -63,8 +63,16 @@ __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free)
 	curr = iovad->cached32_node;
 	cached_iova = container_of(curr, struct iova, node);
 
-	if (free->pfn_lo >= cached_iova->pfn_lo)
-		iovad->cached32_node = rb_next(&free->node);
+	if (free->pfn_lo >= cached_iova->pfn_lo) {
+		struct rb_node *node = rb_next(&free->node);
+		struct iova *iova = container_of(node, struct iova, node);
+
+		/* only cache if it's below 32bit pfn */
+		if (iova->pfn_lo < iovad->dma_32bit_pfn)
+			iovad->cached32_node = node;
+		else
+			iovad->cached32_node = NULL;
+	}
 }
 
 /* Computes the padding size required, to make the
-- 
1.7.4
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