ANDROID: GKI: Add to task_struct size via cmdline

To reduce the size of vendor data allocated in the task_struct, from 512
bytes to a significantly lower 48 bytes, the move to a dynamically sized
task_struct is being made.
As part of this effort, provide means for vendors to pass a size value
via kernel cmdline. Use the passed value to dynamically add to the
task_struct size to accommodate vendor data.
The cmdline parameter to be used is 'android_task_struct_vendor_size'.
For eg., vendors can add the following to the bootargs section of their
devicetree to add an extra 512 bytes to the task_struct:
"android_task_struct_vendor_size=512"
To access this additional memory, use the android_task_vendor_data
function provided.

Bug: 233921394
Change-Id: I6d5ab92080b82f29bbe9735d40f7d0b1e5bb5913
Signed-off-by: Sai Harshini Nimmala <quic_snimmala@quicinc.com>

arch/x86/kernel/fpu/init.c

@@ -173,6 +173,10 @@ static void __init fpu__init_task_struct_size(void)
 	CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
 	CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 
+	if (arch_task_struct_size > sizeof(struct task_struct)) {
+		pr_warn("WARNING: Extra space requested by android_arch_task_struct_size overwritten by %s\n",
+			__func__);
+	}
 	arch_task_struct_size = task_size;
 }
 

kernel/fork.c

@@ -1034,6 +1034,24 @@ static void __init set_max_threads(unsigned int max_threads_suggested)
 #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
 /* Initialized by the architecture: */
 int arch_task_struct_size __read_mostly;
+
+static int __init arch_task_struct_size_setup(char *str)
+{
+	u64 size;
+
+	if (!str)
+		return -EINVAL;
+
+	size = memparse(str, &str);
+
+	if (size < 0 || size > CONFIG_GKI_TASK_STRUCT_VENDOR_SIZE_MAX)
+		return -EINVAL;
+
+	arch_task_struct_size = sizeof(struct task_struct) + size;
+
+	return 0;
+}
+early_param("android_task_struct_vendor_size", arch_task_struct_size_setup);
 #endif
 
 static void __init task_struct_whitelist(unsigned long *offset, unsigned long *size)

kernel/sched/sched.h

@@ -3865,4 +3865,12 @@ void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx);
 
 #include "ext.h"
 
+static inline void *android_task_vendor_data(struct task_struct *p)
+{
+	if (p == &init_task)
+		return &vendor_data_pad[0];
+
+	return p + 1;
+}
+
 #endif /* _KERNEL_SCHED_SCHED_H */