diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 0e67f1721a3d980de842052cb37006492769e6d3..a286c5404ea7011855630d5828e7093746c02b75 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -199,6 +199,18 @@ static phys_addr_t iopte_to_paddr(arm_lpae_iopte pte,
 	return (paddr | (paddr << (48 - 12))) & (ARM_LPAE_PTE_ADDR_MASK << 4);
 }
 
+/*
+ * Convert an index returned by ARM_LPAE_PGD_IDX(), which can point into
+ * a concatenated PGD, into the maximum number of entries that can be
+ * mapped in the same table page.
+ */
+static inline int arm_lpae_max_entries(int i, struct arm_lpae_io_pgtable *data)
+{
+	int ptes_per_table = ARM_LPAE_PTES_PER_TABLE(data);
+
+	return ptes_per_table - (i & (ptes_per_table - 1));
+}
+
 static bool selftest_running = false;
 
 static dma_addr_t __arm_lpae_dma_addr(void *pages)
@@ -390,7 +402,7 @@ static int __arm_lpae_map(struct arm_lpae_io_pgtable *data, unsigned long iova,
 
 	/* If we can install a leaf entry at this level, then do so */
 	if (size == block_size) {
-		max_entries = ARM_LPAE_PTES_PER_TABLE(data) - map_idx_start;
+		max_entries = arm_lpae_max_entries(map_idx_start, data);
 		num_entries = min_t(int, pgcount, max_entries);
 		ret = arm_lpae_init_pte(data, iova, paddr, prot, lvl, num_entries, ptep);
 		if (!ret)
@@ -592,7 +604,7 @@ static size_t arm_lpae_split_blk_unmap(struct arm_lpae_io_pgtable *data,
 
 	if (size == split_sz) {
 		unmap_idx_start = ARM_LPAE_LVL_IDX(iova, lvl, data);
-		max_entries = ptes_per_table - unmap_idx_start;
+		max_entries = arm_lpae_max_entries(unmap_idx_start, data);
 		num_entries = min_t(int, pgcount, max_entries);
 	}
 
@@ -650,7 +662,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 
 	/* If the size matches this level, we're in the right place */
 	if (size == ARM_LPAE_BLOCK_SIZE(lvl, data)) {
-		max_entries = ARM_LPAE_PTES_PER_TABLE(data) - unmap_idx_start;
+		max_entries = arm_lpae_max_entries(unmap_idx_start, data);
 		num_entries = min_t(int, pgcount, max_entries);
 
 		/* Find and handle non-leaf entries */