[PATCH v7 11/11] iommu/arm-smmu-v3: Add KUnit unit tests for Runtime PM

[Pranjal Shrivastava <praan@google.com>]

Introduce a 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  | 150 ++++++++++++++++++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   |   1 +
 2 files changed, 151 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..ef9a17343ed8 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"
@@ -771,7 +775,153 @@ static void arm_smmu_v3_invs_test(struct kunit *test)
 	kfree(test_b);
 }
 
+struct arm_smmu_test_pm_context {
+	u32 *mock_prod_reg;
+	u64 *mock_base;
+	unsigned long *mock_valid_map;
+};
+
+/*
+ * Shared helper to allocate and map a fully functional, self-consuming mock
+ * CMDQ. By redirecting both prod_reg and cons_reg to the same memory location,
+ * every producer write is instantly reflected as a consumer completion.
+ */
+static struct arm_smmu_test_pm_context *
+arm_smmu_v3_test_init_mock_cmdq(struct kunit *test, struct arm_smmu_device *smmu)
+{
+	struct arm_smmu_test_pm_context *ctx;
+	struct arm_smmu_cmdq *cmdq = &smmu->cmdq;
+
+	ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, ctx);
+
+	/* Use a standard 1024-entry queue for safe word bitmask alignment */
+	ctx->mock_prod_reg = kunit_kzalloc(test, sizeof(u32), GFP_KERNEL);
+	ctx->mock_base = kunit_kzalloc(test, 1024 * 16, GFP_KERNEL);
+	ctx->mock_valid_map = kunit_kzalloc(test, BITS_TO_LONGS(1024) * sizeof(long), GFP_KERNEL);
+
+	KUNIT_ASSERT_NOT_NULL(test, ctx->mock_prod_reg);
+	KUNIT_ASSERT_NOT_NULL(test, ctx->mock_base);
+	KUNIT_ASSERT_NOT_NULL(test, ctx->mock_valid_map);
+
+	smmu->features = 0;
+	/* 1024 entries */
+	cmdq->q.llq.max_n_shift = 10;
+	/* SMMUv3 commands are 2 dwords (16 bytes) */
+	cmdq->q.ent_dwords = 2;
+	cmdq->q.base = (__le64 *)ctx->mock_base;
+	cmdq->valid_map = (atomic_long_t *)ctx->mock_valid_map;
+
+	/* Self-Consuming, prod == cons always ensures queue empty */
+	cmdq->q.prod_reg = (__force u32 __iomem *)ctx->mock_prod_reg;
+	cmdq->q.cons_reg = (__force u32 __iomem *)ctx->mock_prod_reg;
+
+	/* Initialize memory indices */
+	atomic_set(&cmdq->q.llq.atomic.prod, 0);
+	atomic_set(&cmdq->q.llq.atomic.cons, 0);
+	atomic_set(&cmdq->owner_prod, 0);
+	*ctx->mock_prod_reg = 0;
+
+	return ctx;
+}
+
+struct arm_smmu_test_timer_context {
+	struct kunit *test;
+	struct arm_smmu_device *smmu;
+	struct arm_smmu_test_pm_context *pm_ctx;
+	struct timer_list timer;
+	bool stopped;
+};
+
+/* Asynchronous timer callback running in softirq context */
+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;
+
+	/*
+	 * Asynchronously set the STOP_FLAG (Close the gate).
+	 * Simulate a concurrent runtime suspend event interrupting
+	 * the invalidations happening under active load.
+	 */
+	atomic_or(CMDQ_PROD_STOP_FLAG, &cmdq->q.llq.atomic.prod);
+
+	/* Signal to the main storm loop that suspend has triggered */
+	WRITE_ONCE(ctx->stopped, true);
+}
+
+/*
+ * Verify SMMU PM Runtime gating, elision, and post-suspend resumption
+ * safety sequentially under active stress.
+ */
+static void arm_smmu_v3_test_rpm_stress_race(struct kunit *test)
+{
+	struct arm_smmu_device *smmu = kunit_kzalloc(test, sizeof(*smmu), GFP_KERNEL);
+	struct arm_smmu_test_pm_context *pm_ctx;
+	struct arm_smmu_test_timer_context *timer_ctx;
+	struct arm_smmu_cmdq *cmdq = &smmu->cmdq;
+	struct arm_smmu_cmd cmd = arm_smmu_make_cmd_cfgi_all();
+	u32 stopped_prod;
+	int i, ret;
+
+	KUNIT_ASSERT_NOT_NULL(test, smmu);
+	pm_ctx = arm_smmu_v3_test_init_mock_cmdq(test, smmu);
+
+	timer_ctx = kunit_kmalloc(test, sizeof(*timer_ctx), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, timer_ctx);
+	timer_ctx->test = test;
+	timer_ctx->smmu = smmu;
+	timer_ctx->pm_ctx = pm_ctx;
+	timer_ctx->stopped = false;
+
+	/* Setup the kernel software timer */
+	timer_setup(&timer_ctx->timer, arm_smmu_v3_test_rpm_timer_callback, 0);
+
+	/* Start the timer to fire in 10 jiffies */
+	mod_timer(&timer_ctx->timer, jiffies + msecs_to_jiffies(10));
+
+	/* Execute the unmap storm until the timer triggers */
+	while (!READ_ONCE(timer_ctx->stopped)) {
+		ret = arm_smmu_cmdq_issue_cmdlist(smmu, cmdq, &cmd, 1, false);
+		if (ret != 0) {
+			KUNIT_FAIL(test, "Unmap Storm loop failed to submit cmd list: %d\n", ret);
+			break;
+		}
+
+		usleep_range(50, 100);
+	}
+
+	timer_delete_sync(&timer_ctx->timer);
+
+	/* Establish the globally stable, post-storm register baseline index */
+	stopped_prod = *pm_ctx->mock_prod_reg;
+
+	/*
+	 * Attempt multiple unmaps while the SMMU is disabled (STOP_GATE is set)
+	 * Every single invalidation must be instantly elided, returning 0
+	 * immediately and leaving the mock MMIO register completely frozen.
+	 */
+	for (i = 0; i < 1000; i++) {
+		ret = arm_smmu_cmdq_issue_cmdlist(smmu, cmdq, &cmd, 1, false);
+		if (ret != 0) {
+			KUNIT_FAIL(test, "Gated storm loop failed at iteration %d: %d\n", i, ret);
+			break;
+		}
+	}
+	KUNIT_EXPECT_EQ(test, stopped_prod, *pm_ctx->mock_prod_reg);
+
+	/*
+	 * Clear the STOP_FLAG (resume SMMU). A new invalidation must now
+	 * successfully commit, moving the prod_reg by exactly 1 slot
+	 */
+	atomic_andnot(CMDQ_PROD_STOP_FLAG, &cmdq->q.llq.atomic.prod);
+	KUNIT_EXPECT_EQ(test, 0, arm_smmu_cmdq_issue_cmdlist(smmu, cmdq, &cmd, 1, false));
+	KUNIT_EXPECT_EQ(test, stopped_prod + 1, *pm_ctx->mock_prod_reg);
+}
+
 static struct kunit_case arm_smmu_v3_test_cases[] = {
+	KUNIT_CASE(arm_smmu_v3_test_rpm_stress_race),
 	KUNIT_CASE(arm_smmu_v3_write_ste_test_bypass_to_abort),
 	KUNIT_CASE(arm_smmu_v3_write_ste_test_abort_to_bypass),
 	KUNIT_CASE(arm_smmu_v3_write_ste_test_cdtable_to_abort),
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 d42f78777571..dd7cfd3c16f4 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -871,6 +871,7 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
 	local_irq_restore(flags);
 	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)
-- 
2.54.0.794.g4f17f83d09-goog