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

[Baolu Lu]

On 8/5/26 12:20, 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.

Fixes: 8a1d82462540 ("iommu/vt-d: Multiple descriptors per 
qi_submit_sync()")
Cc: stable@xxxxxxxxxxxxxxx

> Signed-off-by: Guanghui Feng <guanghuifeng@xxxxxxxxxxxxxxxxx>
> Signed-off-by: bikuan.zbk <bikuan.zbk@xxxxxxxxxxxxxxx>
> ---
>   drivers/iommu/intel/dmar.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> index 767ec092accd..8ae513593406 100644
> --- a/drivers/iommu/intel/dmar.c
> +++ b/drivers/iommu/intel/dmar.c
> @@ -1290,8 +1290,13 @@ 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;

How about adding a brief comment like this?

	/*
	 * 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;
>   
>   			/*

Otherwise, this looks good to me.

Thanks,
baolu