[PATCH 3.16.y-ckt 068/216] iommu/vt-d: Fix an off-by-one bug in __domain_mapping()

[Luis Henriques]

3.16.7-ckt4 -stable review patch.  If anyone has any objections, please let me know.

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

From: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>

commit cc4f14aa170d895c9a43bdb56f62070c8a6da908 upstream.

There's an off-by-one bug in function __domain_mapping(), which may
trigger the BUG_ON(nr_pages < lvl_pages) when
	(nr_pages + 1) & superpage_mask == 0

The issue was introduced by commit 9051aa0268dc "intel-iommu: Combine
domain_pfn_mapping() and domain_sg_mapping()", which sets sg_res to
"nr_pages + 1" to avoid some of the 'sg_res==0' code paths.

It's safe to remove extra "+1" because sg_res is only used to calculate
page size now.

Reported-And-Tested-by: Sudeep Dutt <sudeep.dutt@xxxxxxxxx>
Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
Acked-By: David Woodhouse <David.Woodhouse@xxxxxxxxx>
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 drivers/iommu/intel-iommu.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 382c1801a8f1..b36bd2886940 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -1966,7 +1966,7 @@ static int __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
 	struct dma_pte *first_pte = NULL, *pte = NULL;
 	phys_addr_t uninitialized_var(pteval);
 	int addr_width = agaw_to_width(domain->agaw) - VTD_PAGE_SHIFT;
-	unsigned long sg_res;
+	unsigned long sg_res = 0;
 	unsigned int largepage_lvl = 0;
 	unsigned long lvl_pages = 0;
 
@@ -1977,10 +1977,8 @@ static int __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
 
 	prot &= DMA_PTE_READ | DMA_PTE_WRITE | DMA_PTE_SNP;
 
-	if (sg)
-		sg_res = 0;
-	else {
-		sg_res = nr_pages + 1;
+	if (!sg) {
+		sg_res = nr_pages;
 		pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | prot;
 	}
 
-- 
2.1.4

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