Commit 583b24a2 authored by Chris Metcalf's avatar Chris Metcalf
Browse files

arch/tile: adopt prepare_exit_to_usermode() model from x86 



This change is a prerequisite change for TASK_ISOLATION but also
stands on its own for readability and maintainability.  The existing
tile do_work_pending() was called in a loop from assembly on
the slow path; this change moves the loop into C code as well.
For the x86 version see commit c5c46f59 ("x86/entry: Add new,
comprehensible entry and exit handlers written in C").

This change exposes a pre-existing bug on the older tilepro platform;
the singlestep processing is done last, but on tilepro (unlike tilegx)
we enable interrupts while doing that processing, so we could in
theory miss a signal or other asynchronous event.  A future change
could fix this by breaking the singlestep work into a "prepare"
step done in the main loop, and a "trigger" step done after exiting
the loop.  Since this change is intended as purely a restructuring
change, we call out the bug explicitly now, but don't yet fix it.

Signed-off-by: default avatarChris Metcalf <cmetcalf@ezchip.com>
parent 65a792e8

arch/tile/include/asm/processor.h

+1 −1
Original line number Diff line number Diff line
@@ -212,7 +212,7 @@ static inline void release_thread(struct task_struct *dead_task) 
	/* Nothing for now */

}



extern int do_work_pending(struct pt_regs *regs, u32 flags);

extern void prepare_exit_to_usermode(struct pt_regs *regs, u32 flags);





/*

arch/tile/include/asm/thread_info.h

+6 −2
Original line number Diff line number Diff line
@@ -140,10 +140,14 @@ extern void _cpu_idle(void); 
#define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

#define _TIF_NOHZ		(1<<TIF_NOHZ)



/* Work to do as we loop to exit to user space. */

#define _TIF_WORK_MASK \

	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \

	 _TIF_ASYNC_TLB | _TIF_NOTIFY_RESUME)



/* Work to do on any return to user space. */

#define _TIF_ALLWORK_MASK \

	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | _TIF_SINGLESTEP | \

	 _TIF_ASYNC_TLB | _TIF_NOTIFY_RESUME | _TIF_NOHZ)

	(_TIF_WORK_MASK | _TIF_SINGLESTEP | _TIF_NOHZ)



/* Work to do at syscall entry. */

#define _TIF_SYSCALL_ENTRY_WORK \

arch/tile/kernel/intvec_32.S

+14 −32
Original line number Diff line number Diff line
@@ -845,18 +845,6 @@ STD_ENTRY(interrupt_return) 
.Lresume_userspace:

	FEEDBACK_REENTER(interrupt_return)



	/*

	 * Use r33 to hold whether we have already loaded the callee-saves

	 * into ptregs.  We don't want to do it twice in this loop, since

	 * then we'd clobber whatever changes are made by ptrace, etc.

	 * Get base of stack in r32.

	 */

	{

	 GET_THREAD_INFO(r32)

	 movei  r33, 0

	}



.Lretry_work_pending:

	/*

	 * Disable interrupts so as to make sure we don't

	 * miss an interrupt that sets any of the thread flags (like
@@ -867,33 +855,27 @@ STD_ENTRY(interrupt_return) 
	IRQ_DISABLE(r20, r21)

	TRACE_IRQS_OFF  /* Note: clobbers registers r0-r29 */





	/* Check to see if there is any work to do before returning to user. */

	/*

	 * See if there are any work items (including single-shot items)

	 * to do.  If so, save the callee-save registers to pt_regs

	 * and then dispatch to C code.

	 */

	GET_THREAD_INFO(r21)

	{

	 addi   r29, r32, THREAD_INFO_FLAGS_OFFSET

	 moveli r1, lo16(_TIF_ALLWORK_MASK)

	 addi   r22, r21, THREAD_INFO_FLAGS_OFFSET

	 moveli r20, lo16(_TIF_ALLWORK_MASK)

	}

	{

	 lw     r29, r29

	 auli   r1, r1, ha16(_TIF_ALLWORK_MASK)

	 lw     r22, r22

	 auli   r20, r20, ha16(_TIF_ALLWORK_MASK)

	}

	and     r1, r29, r1

	bzt     r1, .Lrestore_all



	/*

	 * Make sure we have all the registers saved for signal

	 * handling, notify-resume, or single-step.  Call out to C

	 * code to figure out exactly what we need to do for each flag bit,

	 * then if necessary, reload the flags and recheck.

	 */

	and     r1, r22, r20

	{

	 PTREGS_PTR(r0, PTREGS_OFFSET_BASE)

	 bnz    r33, 1f

	 bzt    r1, .Lrestore_all

	}

	push_extra_callee_saves r0

	movei   r33, 1

1:	jal     do_work_pending

	bnz     r0, .Lretry_work_pending

	jal     prepare_exit_to_usermode



	/*

	 * In the NMI case we
@@ -1327,7 +1309,7 @@ STD_ENTRY(ret_from_kernel_thread) 
	FEEDBACK_REENTER(ret_from_kernel_thread)

	{

	 movei  r30, 0               /* not an NMI */

	 j      .Lresume_userspace   /* jump into middle of interrupt_return */

	 j      interrupt_return

	}

	STD_ENDPROC(ret_from_kernel_thread)

arch/tile/kernel/intvec_64.S

+15 −34
Original line number Diff line number Diff line
@@ -878,20 +878,6 @@ STD_ENTRY(interrupt_return) 
.Lresume_userspace:

	FEEDBACK_REENTER(interrupt_return)



	/*

	 * Use r33 to hold whether we have already loaded the callee-saves

	 * into ptregs.  We don't want to do it twice in this loop, since

	 * then we'd clobber whatever changes are made by ptrace, etc.

	 */

	{

	 movei  r33, 0

	 move   r32, sp

	}



	/* Get base of stack in r32. */

	EXTRACT_THREAD_INFO(r32)



.Lretry_work_pending:

	/*

	 * Disable interrupts so as to make sure we don't

	 * miss an interrupt that sets any of the thread flags (like
@@ -902,33 +888,28 @@ STD_ENTRY(interrupt_return) 
	IRQ_DISABLE(r20, r21)

	TRACE_IRQS_OFF  /* Note: clobbers registers r0-r29 */





	/* Check to see if there is any work to do before returning to user. */

	/*

	 * See if there are any work items (including single-shot items)

	 * to do.  If so, save the callee-save registers to pt_regs

	 * and then dispatch to C code.

	 */

	move    r21, sp

	EXTRACT_THREAD_INFO(r21)

	{

	 addi   r29, r32, THREAD_INFO_FLAGS_OFFSET

	 moveli r1, hw1_last(_TIF_ALLWORK_MASK)

	 addi   r22, r21, THREAD_INFO_FLAGS_OFFSET

	 moveli r20, hw1_last(_TIF_ALLWORK_MASK)

	}

	{

	 ld     r29, r29

	 shl16insli r1, r1, hw0(_TIF_ALLWORK_MASK)

	 ld     r22, r22

	 shl16insli r20, r20, hw0(_TIF_ALLWORK_MASK)

	}

	and     r1, r29, r1

	beqzt   r1, .Lrestore_all



	/*

	 * Make sure we have all the registers saved for signal

	 * handling or notify-resume.  Call out to C code to figure out

	 * exactly what we need to do for each flag bit, then if

	 * necessary, reload the flags and recheck.

	 */

	and     r1, r22, r20

	{

	 PTREGS_PTR(r0, PTREGS_OFFSET_BASE)

	 bnez   r33, 1f

	 beqzt  r1, .Lrestore_all

	}

	push_extra_callee_saves r0

	movei   r33, 1

1:	jal     do_work_pending

	bnez    r0, .Lretry_work_pending

	jal     prepare_exit_to_usermode



	/*

	 * In the NMI case we
@@ -1411,7 +1392,7 @@ STD_ENTRY(ret_from_kernel_thread) 
	FEEDBACK_REENTER(ret_from_kernel_thread)

	{

	 movei  r30, 0               /* not an NMI */

	 j      .Lresume_userspace   /* jump into middle of interrupt_return */

	 j      interrupt_return

	}

	STD_ENDPROC(ret_from_kernel_thread)

arch/tile/kernel/process.c

+41 −38
Original line number Diff line number Diff line
@@ -462,54 +462,57 @@ struct task_struct *__sched _switch_to(struct task_struct *prev, 


/*

 * This routine is called on return from interrupt if any of the

 * TIF_WORK_MASK flags are set in thread_info->flags.  It is

 * entered with interrupts disabled so we don't miss an event

 * that modified the thread_info flags.  If any flag is set, we

 * handle it and return, and the calling assembly code will

 * re-disable interrupts, reload the thread flags, and call back

 * if more flags need to be handled.

 *

 * We return whether we need to check the thread_info flags again

 * or not.  Note that we don't clear TIF_SINGLESTEP here, so it's

 * important that it be tested last, and then claim that we don't

 * need to recheck the flags.

 * TIF_ALLWORK_MASK flags are set in thread_info->flags.  It is

 * entered with interrupts disabled so we don't miss an event that

 * modified the thread_info flags.  We loop until all the tested flags

 * are clear.  Note that the function is called on certain conditions

 * that are not listed in the loop condition here (e.g. SINGLESTEP)

 * which guarantees we will do those things once, and redo them if any

 * of the other work items is re-done, but won't continue looping if

 * all the other work is done.

 */

int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)

void prepare_exit_to_usermode(struct pt_regs *regs, u32 thread_info_flags)

{

	/* If we enter in kernel mode, do nothing and exit the caller loop. */

	if (!user_mode(regs))

		return 0;



	user_exit();

	if (WARN_ON(!user_mode(regs)))

		return;



	/* Enable interrupts; they are disabled again on return to caller. */

	do {

		local_irq_enable();



	if (thread_info_flags & _TIF_NEED_RESCHED) {

		if (thread_info_flags & _TIF_NEED_RESCHED)

			schedule();

		return 1;

	}



#if CHIP_HAS_TILE_DMA()

	if (thread_info_flags & _TIF_ASYNC_TLB) {

		if (thread_info_flags & _TIF_ASYNC_TLB)

			do_async_page_fault(regs);

		return 1;

	}

#endif

	if (thread_info_flags & _TIF_SIGPENDING) {



		if (thread_info_flags & _TIF_SIGPENDING)

			do_signal(regs);

		return 1;

	}



		if (thread_info_flags & _TIF_NOTIFY_RESUME) {

			clear_thread_flag(TIF_NOTIFY_RESUME);

			tracehook_notify_resume(regs);

		return 1;

		}

	if (thread_info_flags & _TIF_SINGLESTEP)



		local_irq_disable();

		thread_info_flags = READ_ONCE(current_thread_info()->flags);



	} while (thread_info_flags & _TIF_WORK_MASK);



	if (thread_info_flags & _TIF_SINGLESTEP) {

		single_step_once(regs);

#ifndef __tilegx__

		/*

		 * FIXME: on tilepro, since we enable interrupts in

		 * this routine, it's possible that we miss a signal

		 * or other asynchronous event.

		 */

		local_irq_disable();

#endif

	}



	user_enter();



	return 0;

}



unsigned long get_wchan(struct task_struct *p)

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