iommu/vt-d: use dedicated bitmap to track remapping entry allocation status

Currently Intel interrupt remapping drivers uses the "present" flag bit
in remapping entry to track whether an entry is allocated or not.
It works as follow:
1) allocate a remapping entry and set its "present" flag bit to 1
2) compose other fields for the entry
3) update the remapping entry with the composed value

The remapping hardware may access the entry between step 1 and step 3,
which then observers an entry with the "present" flag set but random
values in all other fields.

This patch introduces a dedicated bitmap to track remapping entry
allocation status instead of sharing the "present" flag with hardware,
thus eliminate the race window. It also simplifies the implementation.

Tested-and-reviewed-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

drivers/iommu/intel_irq_remapping.c

@@ -72,7 +72,6 @@ static int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
 	u16 index, start_index;
 	unsigned int mask = 0;
 	unsigned long flags;
-	int i;
 
 	if (!count || !irq_iommu)
 		return -1;
@@ -96,32 +95,17 @@ static int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
 	}
 
 	raw_spin_lock_irqsave(&irq_2_ir_lock, flags);
-	do {
-		for (i = index; i < index + count; i++)
-			if  (table->base[i].present)
-				break;
-		/* empty index found */
-		if (i == index + count)
-			break;
-
-		index = (index + count) % INTR_REMAP_TABLE_ENTRIES;
-
-		if (index == start_index) {
-			raw_spin_unlock_irqrestore(&irq_2_ir_lock, flags);
-			printk(KERN_ERR "can't allocate an IRTE\n");
-			return -1;
-		}
-	} while (1);
-
-	for (i = index; i < index + count; i++)
-		table->base[i].present = 1;
-
-	cfg->remapped = 1;
-	irq_iommu->iommu = iommu;
-	irq_iommu->irte_index =  index;
-	irq_iommu->sub_handle = 0;
-	irq_iommu->irte_mask = mask;
-
+	index = bitmap_find_free_region(table->bitmap,
+					INTR_REMAP_TABLE_ENTRIES, mask);
+	if (index < 0) {
+		pr_warn("IR%d: can't allocate an IRTE\n", iommu->seq_id);
+	} else {
+		cfg->remapped = 1;
+		irq_iommu->iommu = iommu;
+		irq_iommu->irte_index =  index;
+		irq_iommu->sub_handle = 0;
+		irq_iommu->irte_mask = mask;
+	}
 	raw_spin_unlock_irqrestore(&irq_2_ir_lock, flags);
 
 	return index;
@@ -254,6 +238,8 @@ static int clear_entries(struct irq_2_iommu *irq_iommu)
 		set_64bit(&entry->low, 0);
 		set_64bit(&entry->high, 0);
 	}
+	bitmap_release_region(iommu->ir_table->bitmap, index,
+			      irq_iommu->irte_mask);
 
 	return qi_flush_iec(iommu, index, irq_iommu->irte_mask);
 }
@@ -453,6 +439,7 @@ static int intel_setup_irq_remapping(struct intel_iommu *iommu, int mode)
 {
 	struct ir_table *ir_table;
 	struct page *pages;
+	unsigned long *bitmap;
 
 	ir_table = iommu->ir_table = kzalloc(sizeof(struct ir_table),
 					     GFP_ATOMIC);
@@ -464,13 +451,23 @@ static int intel_setup_irq_remapping(struct intel_iommu *iommu, int mode)
 				 INTR_REMAP_PAGE_ORDER);
 
 	if (!pages) {
-		printk(KERN_ERR "failed to allocate pages of order %d\n",
-		       INTR_REMAP_PAGE_ORDER);
+		pr_err("IR%d: failed to allocate pages of order %d\n",
+		       iommu->seq_id, INTR_REMAP_PAGE_ORDER);
 		kfree(iommu->ir_table);
 		return -ENOMEM;
 	}
 
+	bitmap = kcalloc(BITS_TO_LONGS(INTR_REMAP_TABLE_ENTRIES),
+			 sizeof(long), GFP_ATOMIC);
+	if (bitmap == NULL) {
+		pr_err("IR%d: failed to allocate bitmap\n", iommu->seq_id);
+		__free_pages(pages, INTR_REMAP_PAGE_ORDER);
+		kfree(ir_table);
+		return -ENOMEM;
+	}
+
 	ir_table->base = page_address(pages);
+	ir_table->bitmap = bitmap;
 
 	iommu_set_irq_remapping(iommu, mode);
 	return 0;

include/linux/intel-iommu.h

@@ -288,6 +288,7 @@ struct q_inval {
 
 struct ir_table {
 	struct irte *base;
+	unsigned long *bitmap;
 };
 #endif