powerpc/kernel/iommu: Add new iommu_table_in_use() helper

Having a function to check if the iommu table has any allocation helps
deciding if a tbl can be reset for using a new DMA window.

It should be enough to replace all instances of !bitmap_empty(tbl...).

iommu_table_in_use() skips reserved memory, so we don't need to worry about
releasing it before testing. This causes iommu_table_release_pages() to
become unnecessary, given it is only used to remove reserved memory for
testing.

Also, only allow storing reserved memory values in tbl if they are valid
in the table, so there is no need to check it in the new helper.

Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210817063929.38701-3-leobras.c@gmail.com

arch/powerpc/include/asm/iommu.h

@@ -154,6 +154,7 @@ extern int iommu_tce_table_put(struct iommu_table *tbl);
  */
 extern struct iommu_table *iommu_init_table(struct iommu_table *tbl,
 		int nid, unsigned long res_start, unsigned long res_end);
+bool iommu_table_in_use(struct iommu_table *tbl);
 
 #define IOMMU_TABLE_GROUP_MAX_TABLES	2
 

arch/powerpc/kernel/iommu.c

@@ -690,32 +690,24 @@ static void iommu_table_reserve_pages(struct iommu_table *tbl,
 	if (tbl->it_offset == 0)
 		set_bit(0, tbl->it_map);
 
-	tbl->it_reserved_start = res_start;
-	tbl->it_reserved_end = res_end;
-
-	/* Check if res_start..res_end isn't empty and overlaps the table */
-	if (res_start && res_end &&
-			(tbl->it_offset + tbl->it_size < res_start ||
-			 res_end < tbl->it_offset))
-		return;
+	if (res_start < tbl->it_offset)
+		res_start = tbl->it_offset;
 
-	for (i = tbl->it_reserved_start; i < tbl->it_reserved_end; ++i)
-		set_bit(i - tbl->it_offset, tbl->it_map);
-}
+	if (res_end > (tbl->it_offset + tbl->it_size))
+		res_end = tbl->it_offset + tbl->it_size;
 
-static void iommu_table_release_pages(struct iommu_table *tbl)
-{
-	int i;
+	/* Check if res_start..res_end is a valid range in the table */
+	if (res_start >= res_end) {
+		tbl->it_reserved_start = tbl->it_offset;
+		tbl->it_reserved_end = tbl->it_offset;
+		return;
+	}
 
-	/*
-	 * In case we have reserved the first bit, we should not emit
-	 * the warning below.
-	 */
-	if (tbl->it_offset == 0)
-		clear_bit(0, tbl->it_map);
+	tbl->it_reserved_start = res_start;
+	tbl->it_reserved_end = res_end;
 
 	for (i = tbl->it_reserved_start; i < tbl->it_reserved_end; ++i)
-		clear_bit(i - tbl->it_offset, tbl->it_map);
+		set_bit(i - tbl->it_offset, tbl->it_map);
 }
 
 /*
@@ -779,6 +771,22 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid,
 	return tbl;
 }
 
+bool iommu_table_in_use(struct iommu_table *tbl)
+{
+	unsigned long start = 0, end;
+
+	/* ignore reserved bit0 */
+	if (tbl->it_offset == 0)
+		start = 1;
+	end = tbl->it_reserved_start - tbl->it_offset;
+	if (find_next_bit(tbl->it_map, end, start) != end)
+		return true;
+
+	start = tbl->it_reserved_end - tbl->it_offset;
+	end = tbl->it_size;
+	return find_next_bit(tbl->it_map, end, start) != end;
+}
+
 static void iommu_table_free(struct kref *kref)
 {
 	struct iommu_table *tbl;
@@ -795,10 +803,8 @@ static void iommu_table_free(struct kref *kref)
 
 	iommu_debugfs_del(tbl);
 
-	iommu_table_release_pages(tbl);
-
 	/* verify that table contains no entries */
-	if (!bitmap_empty(tbl->it_map, tbl->it_size))
+	if (iommu_table_in_use(tbl))
 		pr_warn("%s: Unexpected TCEs\n", __func__);
 
 	/* free bitmap */
@@ -1099,14 +1105,9 @@ int iommu_take_ownership(struct iommu_table *tbl)
 	for (i = 0; i < tbl->nr_pools; i++)
 		spin_lock_nest_lock(&tbl->pools[i].lock, &tbl->large_pool.lock);
 
-	iommu_table_release_pages(tbl);
-
-	if (!bitmap_empty(tbl->it_map, tbl->it_size)) {
+	if (iommu_table_in_use(tbl)) {
 		pr_err("iommu_tce: it_map is not empty");
 		ret = -EBUSY;
-		/* Undo iommu_table_release_pages, i.e. restore bit#0, etc */
-		iommu_table_reserve_pages(tbl, tbl->it_reserved_start,
-				tbl->it_reserved_end);
 	} else {
 		memset(tbl->it_map, 0xff, sz);
 	}