iommu/vt-d: Clear PRQ overflow only when PRQ is empty

[ Upstream commit 28a7718 ] It is incorrect to always clear PRO when it's set w/o first checking whether the overflow condition has been cleared. Current code assumes that if an overflow condition occurs it must have been cleared by earlier loop. However since the code runs in a threaded context, the overflow condition could occur even after setting the head to the tail under some extreme condition. To be sane, we should read both head/tail again when seeing a pending PRO and only clear PRO after all pending PRs have been handled. Suggested-by: Kevin Tian <[email protected]> Signed-off-by: Lu Baolu <[email protected]> Link: https://lore.kernel.org/linux-iommu/MWHPR11MB18862D2EA5BD432BF22D99A48CA09@MWHPR11MB1886.namprd11.prod.outlook.com/ Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Joerg Roedel <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
vvavrychuk · Mar 17, 2021 · 1e5ac05 · 1e5ac05
1 parent 82d6c12
commit 1e5ac05
Showing 1 changed file with 11 additions and 2 deletions.
diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
@@ -1079,8 +1079,17 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 	 * Clear the page request overflow bit and wake up all threads that
 	 * are waiting for the completion of this handling.
 	 */
-	if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO)
-		writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG);
+	if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO) {
+		pr_info_ratelimited("IOMMU: %s: PRQ overflow detected\n",
+				    iommu->name);
+		head = dmar_readq(iommu->reg + DMAR_PQH_REG) & PRQ_RING_MASK;
+		tail = dmar_readq(iommu->reg + DMAR_PQT_REG) & PRQ_RING_MASK;
+		if (head == tail) {
+			writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG);
+			pr_info_ratelimited("IOMMU: %s: PRQ overflow cleared",
+					    iommu->name);
+		}
+	}
 
 	if (!completion_done(&iommu->prq_complete))
 		complete(&iommu->prq_complete);