arm64: Use generic kernel_thread() implementation

This patch enables CONFIG_GENERIC_KERNEL_THREAD on arm64, changes
copy_threads to cope with kernel threads creation and adapts
ret_from_fork accordingly. The arm64-specific kernel_thread
implementation is no longer needed.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

4 files changed, 29 insertions, 59 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7ff68c946073..4077b71b1258 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -6,6 +6,7 @@ config ARM64
         select GENERIC_IOMAP
         select GENERIC_IRQ_PROBE
         select GENERIC_IRQ_SHOW
+        select GENERIC_KERNEL_THREAD
         select GENERIC_SMP_IDLE_THREAD
         select GENERIC_TIME_VSYSCALL
         select HARDIRQS_SW_RESEND
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 39a208a392f7..d6331acaf64e 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -136,11 +136,6 @@ unsigned long get_wchan(struct task_struct *p);
 extern struct task_struct *cpu_switch_to(struct task_struct *prev,
                                          struct task_struct *next);
 
-/*
- * Create a new kernel thread
- */
-extern int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
-
 #define task_pt_regs(p) \
         ((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)
 
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index a6f3f7da6880..08db8972ebcc 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -611,7 +611,10 @@ ENDPROC(ret_to_user)
  */
 ENTRY(ret_from_fork)
         bl      schedule_tail
-        get_thread_info tsk
+        cbz     x19, 1f                         // not a kernel thread
+        mov     x0, x20
+        blr     x19
+1:      get_thread_info tsk
         b       ret_to_user
 ENDPROC(ret_from_fork)
 
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f22965ea1cfc..bf615e212c6c 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -240,27 +240,35 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
         struct pt_regs *childregs = task_pt_regs(p);
         unsigned long tls = p->thread.tp_value;
 
-        *childregs = *regs;
-        childregs->regs[0] = 0;
+        memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));
 
-        if (is_compat_thread(task_thread_info(p)))
-                childregs->compat_sp = stack_start;
-        else {
+        if (likely(regs)) {
+                *childregs = *regs;
+                childregs->regs[0] = 0;
+                if (is_compat_thread(task_thread_info(p))) {
+                        childregs->compat_sp = stack_start;
+                } else {
+                        /*
+                         * Read the current TLS pointer from tpidr_el0 as it may be
+                         * out-of-sync with the saved value.
+                         */
+                        asm("mrs %0, tpidr_el0" : "=r" (tls));
+                        childregs->sp = stack_start;
+                }
                 /*
-                 * Read the current TLS pointer from tpidr_el0 as it may be
-                 * out-of-sync with the saved value.
+                 * If a TLS pointer was passed to clone (4th argument), use it
+                 * for the new thread.
                  */
-                asm("mrs %0, tpidr_el0" : "=r" (tls));
-                childregs->sp = stack_start;
+                if (clone_flags & CLONE_SETTLS)
+                        tls = regs->regs[3];
+        } else {
+                memset(childregs, 0, sizeof(struct pt_regs));
+                childregs->pstate = PSR_MODE_EL1h;
+                p->thread.cpu_context.x19 = stack_start;
+                p->thread.cpu_context.x20 = stk_sz;
         }
-
-        memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));
-        p->thread.cpu_context.sp = (unsigned long)childregs;
         p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
-
-        /* If a TLS pointer was passed to clone, use that for the new thread. */
-        if (clone_flags & CLONE_SETTLS)
-                tls = regs->regs[3];
+        p->thread.cpu_context.sp = (unsigned long)childregs;
         p->thread.tp_value = tls;
 
         ptrace_hw_copy_thread(p);
@@ -327,43 +335,6 @@ int dump_fpu (struct pt_regs *regs, struct user_fp *fp)
 }
 EXPORT_SYMBOL(dump_fpu);
 
-/*
- * Shuffle the argument into the correct register before calling the
- * thread function.  x1 is the thread argument, x2 is the pointer to
- * the thread function, and x3 points to the exit function.
- */
-extern void kernel_thread_helper(void);
-asm(    ".section .text\n"
-"       .align\n"
-"       .type   kernel_thread_helper, #function\n"
-"kernel_thread_helper:\n"
-"       mov     x0, x1\n"
-"       mov     x30, x3\n"
-"       br      x2\n"
-"       .size   kernel_thread_helper, . - kernel_thread_helper\n"
-"       .previous");
-
-#define kernel_thread_exit      do_exit
-
-/*
- * Create a kernel thread.
- */
-pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
-{
-        struct pt_regs regs;
-
-        memset(&regs, 0, sizeof(regs));
-
-        regs.regs[1] = (unsigned long)arg;
-        regs.regs[2] = (unsigned long)fn;
-        regs.regs[3] = (unsigned long)kernel_thread_exit;
-        regs.pc = (unsigned long)kernel_thread_helper;
-        regs.pstate = PSR_MODE_EL1h;
-
-        return do_fork(flags|CLONE_VM|CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
-}
-EXPORT_SYMBOL(kernel_thread);
-
 unsigned long get_wchan(struct task_struct *p)
 {
         struct stackframe frame;