Commit eed7c420 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc: copy_thread differentiate kthreads and user mode threads 



When copy_thread is given a kernel function to run in arg->fn, this
does not necessarily mean it is a kernel thread. User threads can be
created this way (e.g., kernel_init, see also x86's copy_thread()).
These threads run a kernel function which may call kernel_execve()
and return, which returns like a userspace exec(2) syscall.

Kernel threads are to  be differentiated with PF_KTHREAD, will always
have arg->fn set, and should never return from that function, instead
calling kthread_exit() to exit.

Create separate paths for the kthread and user kernel thread creation
logic. The kthread path will never exit and does not require a user
interrupt frame, so it gets a minimal stack frame.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-6-npiggin@gmail.com
parent 5088a624

arch/powerpc/include/asm/thread_info.h

+2 −0
Original line number Diff line number Diff line
@@ -176,9 +176,11 @@ static inline bool test_thread_local_flags(unsigned int flags) 
#ifdef CONFIG_COMPAT

#define is_32bit_task()	(test_thread_flag(TIF_32BIT))

#define is_tsk_32bit_task(tsk)	(test_tsk_thread_flag(tsk, TIF_32BIT))

#define clear_tsk_compat_task(tsk) (clear_tsk_thread_flag(p, TIF_32BIT))

#else

#define is_32bit_task()	(IS_ENABLED(CONFIG_PPC32))

#define is_tsk_32bit_task(tsk)	(IS_ENABLED(CONFIG_PPC32))

#define clear_tsk_compat_task(tsk) do { } while (0)

#endif



#if defined(CONFIG_PPC64)

arch/powerpc/kernel/process.c

+62 −36
Original line number Diff line number Diff line
@@ -1738,10 +1738,7 @@ static void setup_ksp_vsid(struct task_struct *p, unsigned long sp) 
 */

int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)

{

	unsigned long clone_flags = args->flags;

	unsigned long usp = args->stack;

	unsigned long tls = args->tls;

	struct pt_regs *childregs, *kregs;

	struct pt_regs *kregs; /* Switch frame regs */

	extern void ret_from_fork(void);

	extern void ret_from_fork_scv(void);

	extern void ret_from_kernel_thread(void);
@@ -1754,33 +1751,56 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 


	klp_init_thread_info(p);



	/* Create initial stack frame. */

	if (unlikely(p->flags & PF_KTHREAD)) {

		/* kernel thread */



		/* Create initial minimum stack frame. */

		sp -= STACK_FRAME_MIN_SIZE;

		((unsigned long *)sp)[0] = 0;



		f = ret_from_kernel_thread;

		p->thread.regs = NULL;	/* no user register state */

		clear_tsk_compat_task(p);

	} else {

		/* user thread */

		struct pt_regs *childregs;



		/* Create initial user return stack frame. */

		sp -= STACK_USER_INT_FRAME_SIZE;

		*(unsigned long *)(sp + STACK_INT_FRAME_MARKER) = STACK_FRAME_REGS_MARKER;



	/* Copy registers */

		childregs = (struct pt_regs *)(sp + STACK_INT_FRAME_REGS);



		if (unlikely(args->fn)) {

		/* kernel thread */

			/*

			 * A user space thread, but it first runs a kernel

			 * thread, and then returns as though it had called

			 * execve rather than fork, so user regs will be

			 * filled in (e.g., by kernel_execve()).

			 */

			((unsigned long *)sp)[0] = 0;

			memset(childregs, 0, sizeof(struct pt_regs));

		childregs->gpr[1] = sp + STACK_USER_INT_FRAME_SIZE;

#ifdef CONFIG_PPC64

		clear_tsk_thread_flag(p, TIF_32BIT);

			childregs->softe = IRQS_ENABLED;

#endif

		p->thread.regs = NULL;	/* no user register state */

			ti->flags |= _TIF_RESTOREALL;

			f = ret_from_kernel_thread;

		} else {

		/* user thread */

			struct pt_regs *regs = current_pt_regs();

			unsigned long clone_flags = args->flags;

			unsigned long usp = args->stack;



			/* Copy registers */

			*childregs = *regs;

			if (usp)

				childregs->gpr[1] = usp;

			((unsigned long *)sp)[0] = childregs->gpr[1];

		p->thread.regs = childregs;

#ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG

			WARN_ON_ONCE(childregs->softe != IRQS_ENABLED);

#endif

			if (clone_flags & CLONE_SETTLS) {

				unsigned long tls = args->tls;



				if (!is_32bit_task())

					childregs->gpr[13] = tls;

				else
@@ -1792,7 +1812,15 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
			else

				f = ret_from_fork;

		}



#ifdef CONFIG_PPC64

		if (cpu_has_feature(CPU_FTR_HAS_PPR))

			childregs->ppr = DEFAULT_PPR;

#endif



		childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);

		p->thread.regs = childregs;

	}



	/*

	 * The way this works is that at some point in the future
@@ -1843,8 +1871,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
		p->thread.dscr_inherit = current->thread.dscr_inherit;

		p->thread.dscr = mfspr(SPRN_DSCR);

	}

	if (cpu_has_feature(CPU_FTR_HAS_PPR))

		childregs->ppr = DEFAULT_PPR;



	p->thread.tidr = 0;

#endif