ANDROID: GKI: Enable the option to alter task_struct size dynamically

Enable the config option that allows for dynamic sizing of the
task_struct. Once config option is enabled, ensure that
arch_task_struct_size is initialized to hold a valid task_struct size.
The motivation behind this change is to reduce the static memory added to
the task_struct to accommodate vendor data.

Bug: 233921394
Signed-off-by: Sai Harshini Nimmala <[email protected]>
Change-Id: Iebc422ba4c650864f470078220b99546e56302f3

Author: Sai Harshini Nimmala

init/Kconfig.gki

@@ -246,6 +246,21 @@ config GKI_HIDDEN_DMA_CONFIGS
 	  Dummy config option used to enable the hidden DMA configs,
 	  required by various SoC platforms.
 
+config GKI_DYNAMIC_TASK_STRUCT_SIZE
+	bool "Dynamic task_struct size needed for GKI"
+	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
+	help
+	  Avoid static allocation of memory for vendor data in task_struct.
+
+config GKI_TASK_STRUCT_VENDOR_SIZE_MAX
+	int "Max vendor data size in bytes"
+	default 512
+	depends on GKI_DYNAMIC_TASK_STRUCT_SIZE
+	help
+	  Allows vendor to choose the maximum size which can be added to
+	  task_struct dynamically when the GKI_DYNAMIC_TASK_STRUCT_SIZE
+	  option is enabled.
+
 # Atrocities needed for
 # a) building GKI modules in separate tree, or
 # b) building drivers that are not modularizable
@@ -279,6 +294,7 @@ config GKI_HACKS_TO_FIX
 	select GKI_HIDDEN_MM_CONFIGS
 	select GKI_HIDDEN_ETHERNET_CONFIGS
 	select GKI_HIDDEN_DMA_CONFIGS
+	select GKI_DYNAMIC_TASK_STRUCT_SIZE
 
 	help
 	  Dummy config option used to enable core functionality used by

init/main.c

@@ -899,6 +899,13 @@ static void __init early_numa_node_init(void)
 #endif
 }
 
+#ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
+static void __init setup_arch_task_struct_size(void)
+{
+	arch_task_struct_size = sizeof(struct task_struct);
+}
+#endif
+
 asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
 void start_kernel(void)
 {
@@ -922,6 +929,9 @@ void start_kernel(void)
 	boot_cpu_init();
 	page_address_init();
 	pr_notice("%s", linux_banner);
+#ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
+        setup_arch_task_struct_size();
+#endif
 	setup_arch(&command_line);
 	/* Static keys and static calls are needed by LSMs */
 	jump_label_init();