iommu/vt-d: Ratelimit fault handler

commit c43fce4e upstream.

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>
Fixes: 0ac2491f ('x86, dmar: move page fault handling code to dmar.c')
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/iommu/dmar.c

@@ -1482,10 +1482,17 @@ 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 */
@@ -1507,6 +1514,7 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
 		if (!(data & DMA_FRCD_F))
 			break;
 
+		if (!ratelimited) {
 			fault_reason = dma_frcd_fault_reason(data);
 			type = dma_frcd_type(data);
 
@@ -1517,12 +1525,15 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
 			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);
 
+		if (!ratelimited)
 			dmar_fault_do_one(iommu, type, fault_reason,
 					  source_id, guest_addr);