From e9bfd64110a660aa71039fc953df580019d8c913 Mon Sep 17 00:00:00 2001
From: Andrew Boie <andrew.p.boie@intel.com>
Date: Fri, 18 Dec 2020 15:18:04 -0800
Subject: [PATCH] mmu: ensure gperf data is mapped

Page tables created at build time may not include the
gperf data at the very end of RAM. Ensure this is mapped
properly at runtime to work around this.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
---
 include/linker/kobject.ld        |  1 +
 include/linker/linker-defs.h     |  1 +
 kernel/include/kernel_internal.h |  3 +++
 kernel/init.c                    |  4 +++-
 kernel/mmu.c                     | 23 +++++++++++++++++++++++
 5 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/linker/kobject.ld b/include/linker/kobject.ld
index d5499efc6e4..c02c10719b6 100644
--- a/include/linker/kobject.ld
+++ b/include/linker/kobject.ld
@@ -5,6 +5,7 @@
  */
 
 #ifdef CONFIG_USERSPACE
+	z_kobject_data_begin = .;
 	/* Constraints:
          *
          * - changes to the size of this section between build phases
diff --git a/include/linker/linker-defs.h b/include/linker/linker-defs.h
index 48d3cc80e38..383fef15e84 100644
--- a/include/linker/linker-defs.h
+++ b/include/linker/linker-defs.h
@@ -303,6 +303,7 @@ extern char z_priv_stacks_ram_start[];
 extern char z_priv_stacks_ram_end[];
 extern char z_user_stacks_start[];
 extern char z_user_stacks_end[];
+extern char z_kobject_data_begin[];
 #endif /* CONFIG_USERSPACE */
 
 #ifdef CONFIG_THREAD_LOCAL_STORAGE
diff --git a/kernel/include/kernel_internal.h b/kernel/include/kernel_internal.h
index 3e0c4f2a455..702d5c512cd 100644
--- a/kernel/include/kernel_internal.h
+++ b/kernel/include/kernel_internal.h
@@ -197,6 +197,9 @@ void z_thread_mark_switched_out(void);
  */
 void z_mem_manage_init(void);
 
+/* Workaround for build-time page table mapping of the kernel */
+void z_kernel_map_fixup(void);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/kernel/init.c b/kernel/init.c
index 7d1ce4a9953..b12db355d86 100644
--- a/kernel/init.c
+++ b/kernel/init.c
@@ -391,7 +391,9 @@ FUNC_NORETURN void z_cstart(void)
 
 	z_dummy_thread_init(&dummy_thread);
 #endif
-
+#if defined(CONFIG_MMU) && defined(CONFIG_USERSPACE)
+	z_kernel_map_fixup();
+#endif
 	/* perform basic hardware initialization */
 	z_sys_init_run_level(_SYS_INIT_LEVEL_PRE_KERNEL_1);
 	z_sys_init_run_level(_SYS_INIT_LEVEL_PRE_KERNEL_2);
diff --git a/kernel/mmu.c b/kernel/mmu.c
index 15d984cade0..9cead314582 100644
--- a/kernel/mmu.c
+++ b/kernel/mmu.c
@@ -453,6 +453,29 @@ size_t k_mem_region_align(uintptr_t *aligned_phys, size_t *aligned_size,
  */
 #define BOOT_VIRT_TO_PHYS(virt) ((uintptr_t)(((uint8_t *)virt) + VM_OFFSET))
 
+#ifdef CONFIG_USERSPACE
+void z_kernel_map_fixup(void)
+{
+	/* XXX: Gperf kernel object data created at build time will not have
+	 * visibility in zephyr_prebuilt.elf. There is a possibility that this
+	 * data would not be memory-mapped if it shifts z_mapped_end between
+	 * builds. Ensure this area is mapped.
+	 *
+	 * A third build phase for page tables would solve this.
+	 */
+	uint8_t *kobject_page_begin =
+		(uint8_t *)ROUND_DOWN((uintptr_t)&z_kobject_data_begin,
+				      CONFIG_MMU_PAGE_SIZE);
+	size_t kobject_size = (size_t)(Z_KERNEL_VIRT_END - kobject_page_begin);
+
+	if (kobject_size != 0) {
+		arch_mem_map(kobject_page_begin,
+			     BOOT_VIRT_TO_PHYS(kobject_page_begin),
+			     kobject_size, K_MEM_PERM_RW | K_MEM_CACHE_WB);
+	}
+}
+#endif /* CONFIG_USERSPACE */
+
 void z_mem_manage_init(void)
 {
 	uintptr_t phys;