[PATCH v10 15/15] iommu/arm-smmu-v3: Add KUnit unit tests for Runtime PM

[Pranjal Shrivastava <praan@google.com>]

Introduce kunit selftests to verify the Runtime PM elision gating,
post-suspend elisions and progress on resumption under active
invalidation load. Simulate concurrent HW suspension using a timer.
Mock all HW registers and CMDQ buffers by allocating them on RAM.
Make the mock CMDQ self-consuming to avoid hitting queue_full scenarios.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 .../iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c  | 215 ++++++++++++++++++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   |   1 +
 2 files changed, 216 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c
index add671363c82..97c1e907717d 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c
@@ -3,6 +3,10 @@
  * Copyright 2024 Google LLC.
  */
 #include <kunit/test.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/sched.h>
+#include <linux/timer.h>
 #include <linux/io-pgtable.h>
 
 #include "arm-smmu-v3.h"
@@ -771,6 +775,215 @@ static void arm_smmu_v3_invs_test(struct kunit *test)
 	kfree(test_b);
 }
 
+struct arm_smmu_mock_cmdq {
+	/*
+	 * Mock register in RAM. Typed as __le32 to match writel_relaxed()
+	 * endianness without calling readl_* accessors directly on RAM.
+	 */
+	__le32 mock_prod_reg;
+};
+
+/* Helper to allocate a self-consuming mock cmdq */
+static void arm_smmu_v3_test_init_mock_cmdq(struct kunit *test,
+					    struct arm_smmu_device *smmu,
+					    struct arm_smmu_mock_cmdq *mock)
+{
+	struct arm_smmu_cmdq *cmdq = &smmu->cmdq;
+	unsigned long *mock_valid_map;
+	u64 *mock_base;
+
+	mock_base = kunit_kzalloc(test, 1024 * sizeof(struct arm_smmu_cmd), GFP_KERNEL);
+	mock_valid_map = kunit_kzalloc(test, BITS_TO_LONGS(1024) * sizeof(long), GFP_KERNEL);
+
+	KUNIT_ASSERT_NOT_NULL(test, mock_base);
+	KUNIT_ASSERT_NOT_NULL(test, mock_valid_map);
+
+	smmu->features = 0;
+	/* 1024 entries */
+	cmdq->q.llq.max_n_shift = 10;
+	cmdq->q.ent_dwords = CMDQ_ENT_DWORDS;
+	cmdq->q.base = (__le64 *)mock_base;
+	cmdq->valid_map = (atomic_long_t *)mock_valid_map;
+
+	/* Self-Consuming, prod == cons always ensures queue empty */
+	cmdq->q.prod_reg = (__force void __iomem *)&mock->mock_prod_reg;
+	cmdq->q.cons_reg = (__force void __iomem *)&mock->mock_prod_reg;
+
+	atomic_set(&cmdq->q.llq.atomic.prod, 0);
+	atomic_set(&cmdq->q.llq.atomic.cons, 0);
+	atomic_set(&cmdq->owner_prod, 0);
+	mock->mock_prod_reg = cpu_to_le32(0);
+}
+
+struct arm_smmu_test_timer_context {
+	struct arm_smmu_device *smmu;
+	struct timer_list timer;
+	bool suspended;
+};
+
+static void arm_smmu_v3_test_rpm_timer_callback(struct timer_list *t)
+{
+	struct arm_smmu_test_timer_context *ctx =
+		timer_container_of(ctx, t, timer);
+	struct arm_smmu_cmdq *cmdq = &ctx->smmu->cmdq;
+
+	/* Simulate a concurrent suspend event interrupting the invalidations */
+	atomic_or(CMDQ_PROD_STOP_FLAG, &cmdq->q.llq.atomic.prod);
+	WRITE_ONCE(ctx->suspended, true);
+}
+
+/*
+ * Verify SMMU PM Runtime gating, elision, and post-suspend resumption
+ * safety sequentially under active stress.
+ */
+static void arm_smmu_v3_rpm_test_stress_race(struct kunit *test)
+{
+	struct arm_smmu_cmd cmd = arm_smmu_make_cmd_cfgi_all();
+	struct arm_smmu_test_timer_context timer_ctx = {0};
+	struct arm_smmu_device mock_smmu = smmu;
+	struct arm_smmu_cmdq *cmdq = &mock_smmu.cmdq;
+	struct arm_smmu_mock_cmdq mock = {0};
+	u32 stopped_prod;
+	int i;
+
+	arm_smmu_v3_test_init_mock_cmdq(test, &mock_smmu, &mock);
+
+	timer_ctx.smmu = &mock_smmu;
+
+	timer_setup_on_stack(&timer_ctx.timer, arm_smmu_v3_test_rpm_timer_callback, 0);
+	mod_timer(&timer_ctx.timer, jiffies + msecs_to_jiffies(10));
+
+	/* Execute the unmap storm until the timer triggers */
+	while (!READ_ONCE(timer_ctx.suspended)) {
+		if (arm_smmu_cmdq_issue_cmdlist(&mock_smmu, cmdq, &cmd, 1, false))
+			break;
+		usleep_range(50, 100);
+	}
+
+	timer_shutdown_sync(&timer_ctx.timer);
+	timer_destroy_on_stack(&timer_ctx.timer);
+
+	/* Establish the post-storm prod_reg index */
+	stopped_prod = le32_to_cpu(mock.mock_prod_reg);
+
+	/*
+	 * Attempt multiple unmaps while the SMMU is disabled (STOP_GATE is set)
+	 * Every single invalidation must get elided and return 0. The prod_reg
+	 * shall remain completely frozen after all of these submissions.
+	 */
+	for (i = 0; i < 1000; i++) {
+		if (arm_smmu_cmdq_issue_cmdlist(&mock_smmu, cmdq, &cmd, 1, false))
+			break;
+	}
+	KUNIT_EXPECT_EQ(test, stopped_prod, le32_to_cpu(mock.mock_prod_reg));
+
+	/*
+	 * Clear the STOP_FLAG (resume the SMMU). A new invalidation must
+	 * now successfully commit prod_idx & move the prod_reg by exactly 1.
+	 */
+	atomic_andnot(CMDQ_PROD_STOP_FLAG, &cmdq->q.llq.atomic.prod);
+	KUNIT_EXPECT_EQ(test, 0, arm_smmu_cmdq_issue_cmdlist(&mock_smmu, cmdq, &cmd, 1, false));
+	KUNIT_EXPECT_EQ(test, Q_POS(&cmdq->q.llq, stopped_prod + 1),
+			le32_to_cpu(mock.mock_prod_reg));
+}
+
+struct arm_smmu_test_kthread_context {
+	struct arm_smmu_device *smmu;
+	int error;
+};
+
+static int arm_smmu_v3_test_kthread_worker(void *data)
+{
+	struct arm_smmu_cmd cmd = arm_smmu_make_cmd_cfgi_all();
+	struct arm_smmu_test_kthread_context *ctx = data;
+	struct arm_smmu_cmdq *cmdq = &ctx->smmu->cmdq;
+
+	while (!kthread_should_stop()) {
+		if (arm_smmu_cmdq_issue_cmdlist(ctx->smmu, cmdq, &cmd, 1, false))
+			WRITE_ONCE(ctx->error, 1);
+		usleep_range(50, 100);
+	}
+	return 0;
+}
+
+KUNIT_DEFINE_ACTION_WRAPPER(kunit_action_kthread_stop, kthread_stop, struct task_struct *);
+
+static void arm_smmu_v3_rpm_test_kthread_race(struct kunit *test)
+{
+	struct arm_smmu_test_kthread_context *ctx;
+	struct arm_smmu_device *mock_smmu;
+	struct arm_smmu_mock_cmdq *mock;
+	struct task_struct *thread1, *thread2;
+	u32 stopped_prod;
+	int i;
+
+	ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+	mock_smmu = kunit_kzalloc(test, sizeof(*mock_smmu), GFP_KERNEL);
+	mock = kunit_kzalloc(test, sizeof(*mock), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, ctx);
+	KUNIT_ASSERT_NOT_NULL(test, mock_smmu);
+	KUNIT_ASSERT_NOT_NULL(test, mock);
+
+	*mock_smmu = smmu;
+	ctx->smmu = mock_smmu;
+	arm_smmu_v3_test_init_mock_cmdq(test, mock_smmu, mock);
+
+	thread1 = kthread_run(arm_smmu_v3_test_kthread_worker, ctx, "smmu_w1");
+	if (IS_ERR(thread1)) {
+		KUNIT_FAIL(test, "Failed to spawn kthread 1\n");
+		return;
+	}
+	if (kunit_add_action_or_reset(test, kunit_action_kthread_stop, thread1)) {
+		KUNIT_FAIL(test, "Failed to register cleanup for kthread 1\n");
+		return;
+	}
+
+	thread2 = kthread_run(arm_smmu_v3_test_kthread_worker, ctx, "smmu_w2");
+	if (IS_ERR(thread2)) {
+		KUNIT_FAIL(test, "Failed to spawn kthread 2\n");
+		return;
+	}
+	if (kunit_add_action_or_reset(test, kunit_action_kthread_stop, thread2)) {
+		KUNIT_FAIL(test, "Failed to register cleanup for kthread 2\n");
+		return;
+	}
+
+	/* Wait for worker threads to start and issue initial commands */
+	for (i = 0; i < 20; i++) {
+		if (le32_to_cpu(READ_ONCE(mock->mock_prod_reg)) > 0)
+			break;
+		usleep_range(1000, 2000);
+	}
+	KUNIT_EXPECT_GT(test, le32_to_cpu(READ_ONCE(mock->mock_prod_reg)), 0);
+
+	/* Gate the CMDQ */
+	atomic_or(CMDQ_PROD_STOP_FLAG, &mock_smmu->cmdq.q.llq.atomic.prod);
+
+	/* Wait for in-flight submissions to settle */
+	for (i = 0; i < 50; i++) {
+		stopped_prod = le32_to_cpu(READ_ONCE(mock->mock_prod_reg));
+		usleep_range(1000, 2000);
+		if (stopped_prod == le32_to_cpu(READ_ONCE(mock->mock_prod_reg)))
+			break;
+	}
+
+	usleep_range(1000, 2000);
+	KUNIT_EXPECT_EQ(test, stopped_prod, le32_to_cpu(READ_ONCE(mock->mock_prod_reg)));
+
+	/* Open the gate and wait for worker threads to resume */
+	atomic_andnot(CMDQ_PROD_STOP_FLAG, &mock_smmu->cmdq.q.llq.atomic.prod);
+	for (i = 0; i < 20; i++) {
+		if (le32_to_cpu(READ_ONCE(mock->mock_prod_reg)) != stopped_prod)
+			break;
+		usleep_range(1000, 2000);
+	}
+	KUNIT_EXPECT_NE(test, stopped_prod, le32_to_cpu(READ_ONCE(mock->mock_prod_reg)));
+
+	kunit_release_action(test, kunit_action_kthread_stop, thread2);
+	kunit_release_action(test, kunit_action_kthread_stop, thread1);
+	KUNIT_EXPECT_EQ(test, 0, READ_ONCE(ctx->error));
+}
+
 static struct kunit_case arm_smmu_v3_test_cases[] = {
 	KUNIT_CASE(arm_smmu_v3_write_ste_test_bypass_to_abort),
 	KUNIT_CASE(arm_smmu_v3_write_ste_test_abort_to_bypass),
@@ -797,6 +1010,8 @@ static struct kunit_case arm_smmu_v3_test_cases[] = {
 	KUNIT_CASE(arm_smmu_v3_write_cd_test_sva_clear),
 	KUNIT_CASE(arm_smmu_v3_write_cd_test_sva_release),
 	KUNIT_CASE(arm_smmu_v3_invs_test),
+	KUNIT_CASE(arm_smmu_v3_rpm_test_stress_race),
+	KUNIT_CASE(arm_smmu_v3_rpm_test_kthread_race),
 	{},
 };
 
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 8e4ce5eb2228..12d191fe57ed 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -991,6 +991,7 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
 
 	return ret;
 }
+EXPORT_SYMBOL_IF_KUNIT(arm_smmu_cmdq_issue_cmdlist);
 
 static int arm_smmu_cmdq_issue_cmd_p(struct arm_smmu_device *smmu,
 				     struct arm_smmu_cmd *cmd, bool sync)
-- 
2.55.0.979.g7e5102b832-goog