[PATCH] iommu/iova: Fix alloc iova overflows issue

[yf.wang at mediatek.com]

From: Yunfei Wang <yf.wang at mediatek.com>

In __alloc_and_insert_iova_range, there is an issue that retry_pfn
overflows. The value of iovad->anchor.pfn_hi is ~0UL, then when
iovad->cached_node is iovad->anchor, curr_iova->pfn_hi + 1 will
overflow. As a result, if the retry logic is executed, low_pfn is
updated to 0, and then new_pfn < low_pfn returns false to make the
allocation successful.

This issue occurs in the following two situations:
1. The first iova size exceeds the domain size. When initializing
iova domain, iovad->cached_node is assigned as iovad->anchor. For
example, the iova domain size is 10M, start_pfn is 0x1_F000_0000,
and the iova size allocated for the first time is 11M. The
following is the log information, new->pfn_lo is smaller than
iovad->cached_node.

Example log:
[  223.798112][T1705487] sh: [name:iova&]__alloc_and_insert_iova_range
start_pfn:0x1f0000,retry_pfn:0x0,size:0xb00,limit_pfn:0x1f0a00
[  223.799590][T1705487] sh: [name:iova&]__alloc_and_insert_iova_range
success start_pfn:0x1f0000,new->pfn_lo:0x1efe00,new->pfn_hi:0x1f08ff

2. The node with the largest iova->pfn_lo value in the iova domain
is deleted, iovad->cached_node will be updated to iovad->anchor,
and then the alloc iova size exceeds the maximum iova size that can
be allocated in the domain.

Adding judgment that retry_pfn must be greater than iovad->start_pfn
can fix this issue.

Signed-off-by: jianjiao zeng <jianjiao.zeng at mediatek.com>
Signed-off-by: Yunfei Wang <yf.wang at mediatek.com>
---
 drivers/iommu/iova.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index a44ad92fc5eb..0073206c2a95 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -209,7 +209,8 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 	} while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= low_pfn);
 
 	if (high_pfn < size || new_pfn < low_pfn) {
-		if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) {
+		if (low_pfn == iovad->start_pfn &&
+		    retry_pfn >= iovad->start_pfn && retry_pfn < limit_pfn) {
 			high_pfn = limit_pfn;
 			low_pfn = retry_pfn;
 			curr = iova_find_limit(iovad, limit_pfn);
-- 
2.18.0