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

[Samiullah Khawaja <skhawaja@google.com>]

On Thu, Aug 20, 2026 at 10:47:41PM +0800, Guanghui Feng wrote:
>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
>
>

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>