[PATCH 2/2] iommupt: add a KUnit test for unmapping an empty range

[YeeLi <seven.yi.lee@gmail.com>]

From: yeeli <seven.yi.lee@gmail.com>

Unmapping a range that holds no mappings must not record anything in
the IOTLB gather. Otherwise iova + len - 1 underflows and the flush
covers the whole domain, or widens a range that was already gathered.

Check that the gather stays empty for a hole at IOVA 0 and at a
non-zero IOVA. Without the previous fix the first case turns the gather
into [0, ULONG_MAX] and the second one flips it to [iova, iova - 1].

Signed-off-by: yeeli <seven.yi.lee@gmail.com>
---
 drivers/iommu/generic_pt/kunit_iommu_pt.h | 31 +++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/iommu/generic_pt/kunit_iommu_pt.h b/drivers/iommu/generic_pt/kunit_iommu_pt.h
index 9fc71db74234..59a9386f1474 100644
--- a/drivers/iommu/generic_pt/kunit_iommu_pt.h
+++ b/drivers/iommu/generic_pt/kunit_iommu_pt.h
@@ -427,6 +427,36 @@ static void test_mixed(struct kunit *test)
 	check_iova(test, start, oa, len);
 }
 
+/*
+ * Unmapping a range that holds no mappings must not record anything in
+ * the IOTLB gather. Otherwise iova + len - 1 underflows and the flush
+ * covers the whole domain, or widens a range that was already gathered.
+ */
+static void test_unmap_hole(struct kunit *test)
+{
+	struct kunit_iommu_priv *priv = test->priv;
+	struct iommu_iotlb_gather gather;
+
+	/* A hole at IOVA 0 must not turn the gather into [0, ULONG_MAX]. */
+	iommu_iotlb_gather_init(&gather);
+	KUNIT_ASSERT_EQ(
+		test,
+		iommu_unmap_fast(&priv->domain, 0, priv->smallest_pgsz, &gather),
+		0);
+	KUNIT_EXPECT_EQ(test, gather.start, ULONG_MAX);
+	KUNIT_EXPECT_EQ(test, gather.end, 0);
+
+	/* Neither may a hole at a non-zero IOVA widen the gather. */
+	iommu_iotlb_gather_init(&gather);
+	KUNIT_ASSERT_EQ(
+		test,
+		iommu_unmap_fast(&priv->domain, priv->smallest_pgsz,
+				 priv->smallest_pgsz, &gather),
+		0);
+	KUNIT_EXPECT_EQ(test, gather.start, ULONG_MAX);
+	KUNIT_EXPECT_EQ(test, gather.end, 0);
+}
+
 static struct kunit_case iommu_test_cases[] = {
 	KUNIT_CASE_FMT(test_increase_level),
 	KUNIT_CASE_FMT(test_map_simple),
@@ -435,6 +465,7 @@ static struct kunit_case iommu_test_cases[] = {
 	KUNIT_CASE_FMT(test_random_map),
 	KUNIT_CASE_FMT(test_pgsize_boundary),
 	KUNIT_CASE_FMT(test_mixed),
+	KUNIT_CASE_FMT(test_unmap_hole),
 	{},
 };
 
-- 
2.34.1