iommu/vt-d: Fix an off-by-one bug in __domain_mapping()

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@intel.com>
Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: <stable@vger.kernel.org> # >= 3.0
Acked-By: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 99bf651234a6..fe6830af6cfa 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -1986,7 +1986,7 @@ 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);
-        unsigned long sg_res;
+        unsigned long sg_res = 0;
         unsigned int largepage_lvl = 0;
         unsigned long lvl_pages = 0;
 
@@ -1997,10 +1997,8 @@ 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;
         }