[PATCH v2 1/2] iommu/vt-d: Ratelimit fault handler

[Alex Williamson <alex.williamson@redhat.com>]

Fault rates can easily overwhelm the console and make the system
unresponsive.  Ratelimit to allow an opportunity for maintenance.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/iommu/dmar.c |   33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 8ffd756..8f8bfff 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -1602,10 +1602,17 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
 	int reg, fault_index;
 	u32 fault_status;
 	unsigned long flag;
+	bool ratelimited;
+	static DEFINE_RATELIMIT_STATE(rs,
+				      DEFAULT_RATELIMIT_INTERVAL,
+				      DEFAULT_RATELIMIT_BURST);
+
+	/* Disable printing, simply clear the fault when ratelimited */
+	ratelimited = !__ratelimit(&rs);
 
 	raw_spin_lock_irqsave(&iommu->register_lock, flag);
 	fault_status = readl(iommu->reg + DMAR_FSTS_REG);
-	if (fault_status)
+	if (fault_status && !ratelimited)
 		pr_err("DRHD: handling fault status reg %x\n", fault_status);
 
 	/* TBD: ignore advanced fault log currently */
@@ -1627,24 +1634,28 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
 		if (!(data & DMA_FRCD_F))
 			break;
 
-		fault_reason = dma_frcd_fault_reason(data);
-		type = dma_frcd_type(data);
+		if (!ratelimited) {
+			fault_reason = dma_frcd_fault_reason(data);
+			type = dma_frcd_type(data);
 
-		data = readl(iommu->reg + reg +
-				fault_index * PRIMARY_FAULT_REG_LEN + 8);
-		source_id = dma_frcd_source_id(data);
+			data = readl(iommu->reg + reg +
+				     fault_index * PRIMARY_FAULT_REG_LEN + 8);
+			source_id = dma_frcd_source_id(data);
+
+			guest_addr = dmar_readq(iommu->reg + reg +
+					fault_index * PRIMARY_FAULT_REG_LEN);
+			guest_addr = dma_frcd_page_addr(guest_addr);
+		}
 
-		guest_addr = dmar_readq(iommu->reg + reg +
-				fault_index * PRIMARY_FAULT_REG_LEN);
-		guest_addr = dma_frcd_page_addr(guest_addr);
 		/* clear the fault */
 		writel(DMA_FRCD_F, iommu->reg + reg +
 			fault_index * PRIMARY_FAULT_REG_LEN + 12);
 
 		raw_spin_unlock_irqrestore(&iommu->register_lock, flag);
 
-		dmar_fault_do_one(iommu, type, fault_reason,
-				source_id, guest_addr);
+		if (!ratelimited)
+			dmar_fault_do_one(iommu, type, fault_reason,
+					  source_id, guest_addr);
 
 		fault_index++;
 		if (fault_index >= cap_num_fault_regs(iommu->cap))