[PATCH] iommu/vt-d: Fix IQE handling to cover all descriptors in submission range

[Guanghui Feng <guanghuifeng@linux.alibaba.com>]

Currently, qi_check_fault() only handles IQE (Invalidation Queue Error)
when the faulting descriptor index exactly matches the first descriptor
of the current submission (head == index). This is too restrictive in
multi-descriptor submissions where the error could occur at any
descriptor within the batch.

If the IQE is triggered by a descriptor that belongs to the current
submission but is not at the starting index, the function returns 0
without clearing the IQE fault status. Since hardware stops fetching
new descriptors until IQE is cleared, this leads to an indefinite wait
on the wait descriptor completion - effectively a deadlock.

Fix this by expanding the IQE handling condition to cover all descriptors
within the circular range [index, wait_index]. Use explicit bounds
checking that properly handles the wrap-around case of the circular
queue.

Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com>
Signed-off-by: bikuan.zbk <bikuan.zbk@alibaba-inc.com>
---
 drivers/iommu/intel/dmar.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index ba675b08cd20..ecc95af06f61 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1366,8 +1366,21 @@ static int qi_check_fault(struct intel_iommu *iommu, int index, int wait_index)
 	 * is cleared.
 	 */
 	if (fault & DMA_FSTS_IQE) {
+		int head_idx;
+
 		head = readl(iommu->reg + DMAR_IQH_REG);
-		if ((head >> shift) == index) {
+		head_idx = head >> shift;
+
+		/*
+		 * The faulting descriptor can be anywhere within the current
+		 * submission's range [index, wait_index]. Since the queue is
+		 * circular, this submission may wrap around QI_LENGTH
+		 * (index > wait_index in that case), so check both the
+		 * non-wrapped and wrapped cases of the range.
+		 */ 
+		if (index <= wait_index ?
+		    (head_idx >= index && head_idx <= wait_index) :
+		    (head_idx >= index || head_idx <= wait_index)) {
 			struct qi_desc *desc = qi->desc + head;
 
 			/*
-- 
2.43.7