tests: arm64: exercize MMU page table allocation and recycling

This code was never formally tested before... and without the preceding
commit it obviously didn't work either.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

arch/arm64/core/mmu.c

@@ -102,6 +102,35 @@ static inline bool is_table_unused(uint64_t *table)
 	return (table_usage(table, 0) & XLAT_PTE_COUNT_MASK) == 0;
 }
 
+#ifdef CONFIG_TEST
+/* Hooks to let test code peek at table states */
+
+int arm64_mmu_nb_free_tables(void)
+{
+	int count = 0;
+
+	for (int i = 0; i < CONFIG_MAX_XLAT_TABLES; i++) {
+		if (xlat_use_count[i] == 0) {
+			count++;
+		}
+	}
+
+	return count;
+}
+
+int arm64_mmu_tables_total_usage(void)
+{
+	int count = 0;
+
+	for (int i = 0; i < CONFIG_MAX_XLAT_TABLES; i++) {
+		count += xlat_use_count[i];
+	}
+
+	return count;
+}
+
+#endif /* CONFIG_TEST */
+
 static inline bool is_free_desc(uint64_t desc)
 {
 	return (desc & PTE_DESC_TYPE_MASK) == PTE_INVALID_DESC;

tests/arch/arm64/arm64_mmu/CMakeLists.txt

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(arm64_mmu)
+
+target_include_directories(app PRIVATE
+  ${ZEPHYR_BASE}/kernel/include
+  ${ZEPHYR_BASE}/arch/${ARCH}/include
+  )
+
+target_sources(app PRIVATE src/main.c)

tests/arch/arm64/arm64_mmu/prj.conf

@@ -0,0 +1,9 @@
+CONFIG_ASSERT=y
+CONFIG_LOG=y
+CONFIG_LOG_MODE_MINIMAL=y
+CONFIG_ZTEST=y
+CONFIG_ARM_MMU=y
+CONFIG_MMU_PAGE_SIZE=0x1000
+CONFIG_ARM64_VA_BITS_36=y
+CONFIG_ARM64_PA_BITS_36=y
+CONFIG_MAX_XLAT_TABLES=8

tests/arch/arm64/arm64_mmu/src/main.c

@@ -0,0 +1,154 @@
+/*
+ * Copyright (c) 2024 BayLibre, SAS
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+#include <zephyr/ztest.h>
+#include <kernel_arch_interface.h>
+
+/*
+ * Virtual and physical addresses used to exercize MMU page table recycling.
+ * Those are completely arbitrary addresses away from any existing addresses
+ * (no worry, the test will fail otherwise). Those addresses don't have
+ * to be valid as we won't attempt any access to the mapped memory.
+ */
+#define TEST_VIRT_ADDR	0x456560000
+#define TEST_PHYS_ADDR	0x123230000
+
+/* special test hooks in arch/arm64/core/mmu.c for test purpose */
+extern int arm64_mmu_nb_free_tables(void);
+extern int arm64_mmu_tables_total_usage(void);
+
+/* initial states to compare against */
+static int initial_nb_free_tables;
+static int initial_tables_usage;
+
+static void *arm64_mmu_test_init(void)
+{
+	/* get initial states */
+	initial_nb_free_tables = arm64_mmu_nb_free_tables();
+	initial_tables_usage = arm64_mmu_tables_total_usage();
+
+	TC_PRINT("  Total page tables:           %d\n", CONFIG_MAX_XLAT_TABLES);
+	TC_PRINT("  Initial free tables:         %d\n", initial_nb_free_tables);
+	TC_PRINT("  Initial total table usage:   %#x\n", initial_tables_usage);
+
+	zassert_true(initial_nb_free_tables > 1,
+		     "initial_nb_free_tables = %d", initial_nb_free_tables);
+	zassert_true(initial_tables_usage > 1,
+		     "initial_tables_usage = %d", initial_tables_usage);
+
+	return NULL;
+}
+
+static int mem_map_test(uintptr_t virt_addr, uintptr_t phys_addr, size_t size)
+{
+	/*
+	 * This is not defined to return any error but the implementation
+	 * will call k_panic() if an error occurs.
+	 */
+	arch_mem_map((void *)virt_addr, phys_addr, size, K_MEM_ARM_NORMAL_NC);
+
+	int mapped_nb_free_tables = arm64_mmu_nb_free_tables();
+	int mapped_tables_usage = arm64_mmu_tables_total_usage();
+
+	TC_PRINT("  After arch_mem_map:\n");
+	TC_PRINT("   current free tables:        %d\n", mapped_nb_free_tables);
+	TC_PRINT("   current total table usage:  %#x\n", mapped_tables_usage);
+
+	zassert_true(mapped_nb_free_tables < initial_nb_free_tables,
+		     "%d vs %d", mapped_nb_free_tables, initial_nb_free_tables);
+	zassert_true(mapped_tables_usage > initial_tables_usage,
+		     "%#x vs %#x", mapped_tables_usage > initial_tables_usage);
+
+	arch_mem_unmap((void *)virt_addr, size);
+
+	int unmapped_nb_free_tables = arm64_mmu_nb_free_tables();
+	int unmapped_tables_usage = arm64_mmu_tables_total_usage();
+
+	TC_PRINT("  After arch_mem_unmap:\n");
+	TC_PRINT("   current free tables:        %d\n", unmapped_nb_free_tables);
+	TC_PRINT("   current total table usage:  %#x\n", unmapped_tables_usage);
+
+	zassert_true(unmapped_nb_free_tables == initial_nb_free_tables,
+		     "%d vs %d", unmapped_nb_free_tables, initial_nb_free_tables);
+	zassert_true(unmapped_tables_usage == initial_tables_usage,
+		     "%#x vs %#x", unmapped_tables_usage > initial_tables_usage);
+
+	int tables_used = unmapped_nb_free_tables - mapped_nb_free_tables;
+	return tables_used;
+}
+
+ZTEST(arm64_mmu, test_arm64_mmu_01_single_page)
+{
+	/*
+	 * Let's map a single page to start with. This will allocate
+	 * multiple tables to reach the deepest level.
+	 */
+	uintptr_t virt = TEST_VIRT_ADDR;
+	uintptr_t phys = TEST_PHYS_ADDR;
+	size_t size    = CONFIG_MMU_PAGE_SIZE;
+
+	int tables_used = mem_map_test(virt, phys, size);
+
+	zassert_true(tables_used == 2, "used %d tables", tables_used);
+}
+
+ZTEST(arm64_mmu, test_arm64_mmu_02_single_block)
+{
+	/*
+	 * Same thing as above, except that we expect a block mapping
+	 * this time. Both addresses and the size must be properly aligned.
+	 * Table allocation won't go as deep as for a page.
+	 */
+	int table_entries = CONFIG_MMU_PAGE_SIZE / sizeof(uint64_t);
+	size_t block_size = table_entries * CONFIG_MMU_PAGE_SIZE;
+	uintptr_t virt = TEST_VIRT_ADDR & ~(block_size - 1);
+	uintptr_t phys = TEST_PHYS_ADDR & ~(block_size - 1);
+
+	int tables_used = mem_map_test(virt, phys, block_size);
+
+	zassert_true(tables_used == 1, "used %d tables", tables_used);
+}
+
+ZTEST(arm64_mmu, test_arm64_mmu_03_block_and_page)
+{
+	/*
+	 * Same thing as above, except that we expect a block mapping
+	 * followed by a page mapping to exercize range splitting.
+	 * To achieve that we simply increase the size by one page and keep
+	 * starting addresses aligned to a block.
+	 */
+	int table_entries = CONFIG_MMU_PAGE_SIZE / sizeof(uint64_t);
+	size_t block_size = table_entries * CONFIG_MMU_PAGE_SIZE;
+	uintptr_t virt = TEST_VIRT_ADDR & ~(block_size - 1);
+	uintptr_t phys = TEST_PHYS_ADDR & ~(block_size - 1);
+	size_t size = block_size + CONFIG_MMU_PAGE_SIZE;
+
+	int tables_used = mem_map_test(virt, phys, size);
+
+	zassert_true(tables_used == 2, "used %d tables", tables_used);
+}
+
+ZTEST(arm64_mmu, test_arm64_mmu_04_page_and_block)
+{
+	/*
+	 * Same thing as above, except that we expect a page mapping
+	 * followed by a block mapping to exercize range splitting.
+	 * To achieve that we increase the size by one page and decrease
+	 * starting addresses by one page below block alignment.
+	 */
+	int table_entries = CONFIG_MMU_PAGE_SIZE / sizeof(uint64_t);
+	size_t block_size = table_entries * CONFIG_MMU_PAGE_SIZE;
+	uintptr_t virt = (TEST_VIRT_ADDR & ~(block_size - 1)) - CONFIG_MMU_PAGE_SIZE;
+	uintptr_t phys = (TEST_PHYS_ADDR & ~(block_size - 1)) - CONFIG_MMU_PAGE_SIZE;
+	size_t size = block_size + CONFIG_MMU_PAGE_SIZE;
+
+	int tables_used = mem_map_test(virt, phys, size);
+
+	zassert_true(tables_used == 2, "used %d tables", tables_used);
+}
+
+ZTEST_SUITE(arm64_mmu, NULL, arm64_mmu_test_init, NULL, NULL, NULL);

tests/arch/arm64/arm64_mmu/testcase.yaml

@@ -0,0 +1,3 @@
+tests:
+  arch.arm64.mmu:
+    platform_allow: qemu_cortex_a53