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Commit cbc9565e authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt
Browse files

powerpc: Remove ksp_limit on ppc64 



We've been keeping that field in thread_struct for a while, it contains
the "limit" of the current stack pointer and is meant to be used for
detecting stack overflows.

It has a few problems however:

 - First, it was never actually *used* on 64-bit. Set and updated but
not actually exploited

 - When switching stack to/from irq and softirq stacks, it's update
is racy unless we hard disable interrupts, which is costly. This
is fine on 32-bit as we don't soft-disable there but not on 64-bit.

Thus rather than fixing 2 in order to implement 1 in some hypothetical
future, let's remove the code completely from 64-bit. In order to avoid
a clutter of ifdef's, we remove the updates from C code completely
during interrupt stack switching, and instead maintain it from the
asm helper that is used to do the stack switching in the first place.

Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 0366a1c7

arch/powerpc/include/asm/processor.h

+1 −3
Original line number Diff line number Diff line
@@ -149,8 +149,6 @@ typedef struct { 


struct thread_struct {

	unsigned long	ksp;		/* Kernel stack pointer */

	unsigned long	ksp_limit;	/* if ksp <= ksp_limit stack overflow */



#ifdef CONFIG_PPC64

	unsigned long	ksp_vsid;

#endif
@@ -162,6 +160,7 @@ struct thread_struct { 
#endif

#ifdef CONFIG_PPC32

	void		*pgdir;		/* root of page-table tree */

	unsigned long	ksp_limit;	/* if ksp <= ksp_limit stack overflow */

#endif

#ifdef CONFIG_PPC_ADV_DEBUG_REGS

	/*
@@ -321,7 +320,6 @@ struct thread_struct { 
#else

#define INIT_THREAD  { \

	.ksp = INIT_SP, \

	.ksp_limit = INIT_SP_LIMIT, \

	.regs = (struct pt_regs *)INIT_SP - 1, /* XXX bogus, I think */ \

	.fs = KERNEL_DS, \

	.fpr = {{0}}, \

arch/powerpc/kernel/asm-offsets.c

+2 −1
Original line number Diff line number Diff line
@@ -80,10 +80,11 @@ int main(void) 
	DEFINE(TASKTHREADPPR, offsetof(struct task_struct, thread.ppr));

#else

	DEFINE(THREAD_INFO, offsetof(struct task_struct, stack));

	DEFINE(THREAD_INFO_GAP, _ALIGN_UP(sizeof(struct thread_info), 16));

	DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit));

#endif /* CONFIG_PPC64 */



	DEFINE(KSP, offsetof(struct thread_struct, ksp));

	DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit));

	DEFINE(PT_REGS, offsetof(struct thread_struct, regs));

#ifdef CONFIG_BOOKE

	DEFINE(THREAD_NORMSAVES, offsetof(struct thread_struct, normsave[0]));

arch/powerpc/kernel/irq.c

+0 −12
Original line number Diff line number Diff line
@@ -496,7 +496,6 @@ void do_IRQ(struct pt_regs *regs) 
{

	struct pt_regs *old_regs = set_irq_regs(regs);

	struct thread_info *curtp, *irqtp;

	unsigned long saved_sp_limit;



	/* Switch to the irq stack to handle this */

	curtp = current_thread_info();
@@ -509,12 +508,6 @@ void do_IRQ(struct pt_regs *regs) 
		return;

	}



	/* Adjust the stack limit */

	saved_sp_limit = current->thread.ksp_limit;

	current->thread.ksp_limit = (unsigned long)irqtp +

		_ALIGN_UP(sizeof(struct thread_info), 16);





	/* Prepare the thread_info in the irq stack */

	irqtp->task = curtp->task;

	irqtp->flags = 0;
@@ -526,7 +519,6 @@ void do_IRQ(struct pt_regs *regs) 
	call_do_irq(regs, irqtp);



	/* Restore stack limit */

	current->thread.ksp_limit = saved_sp_limit;

	irqtp->task = NULL;



	/* Copy back updates to the thread_info */
@@ -604,16 +596,12 @@ void irq_ctx_init(void) 
static inline void do_softirq_onstack(void)

{

	struct thread_info *curtp, *irqtp;

	unsigned long saved_sp_limit = current->thread.ksp_limit;



	curtp = current_thread_info();

	irqtp = softirq_ctx[smp_processor_id()];

	irqtp->task = curtp->task;

	irqtp->flags = 0;

	current->thread.ksp_limit = (unsigned long)irqtp +

				    _ALIGN_UP(sizeof(struct thread_info), 16);

	call_do_softirq(irqtp);

	current->thread.ksp_limit = saved_sp_limit;

	irqtp->task = NULL;



	/* Set any flag that may have been set on the

arch/powerpc/kernel/misc_32.S

+16 −0
Original line number Diff line number Diff line
@@ -36,25 +36,41 @@ 


	.text



/*

 * We store the saved ksp_limit in the unused part

 * of the STACK_FRAME_OVERHEAD

 */

_GLOBAL(call_do_softirq)

	mflr	r0

	stw	r0,4(r1)

	lwz	r10,THREAD+KSP_LIMIT(r2)

	addi	r11,r3,THREAD_INFO_GAP

	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)

	mr	r1,r3

	stw	r10,8(r1)

	stw	r11,THREAD+KSP_LIMIT(r2)

	bl	__do_softirq

	lwz	r10,8(r1)

	lwz	r1,0(r1)

	lwz	r0,4(r1)

	stw	r10,THREAD+KSP_LIMIT(r2)

	mtlr	r0

	blr



_GLOBAL(call_do_irq)

	mflr	r0

	stw	r0,4(r1)

	lwz	r10,THREAD+KSP_LIMIT(r2)

	addi	r11,r3,THREAD_INFO_GAP

	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)

	mr	r1,r4

	stw	r10,8(r1)

	stw	r11,THREAD+KSP_LIMIT(r2)

	bl	__do_irq

	lwz	r10,8(r1)

	lwz	r1,0(r1)

	lwz	r0,4(r1)

	stw	r10,THREAD+KSP_LIMIT(r2)

	mtlr	r0

	blr

arch/powerpc/kernel/process.c

+2 −1
Original line number Diff line number Diff line
@@ -1000,9 +1000,10 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, 
	kregs = (struct pt_regs *) sp;

	sp -= STACK_FRAME_OVERHEAD;

	p->thread.ksp = sp;

#ifdef CONFIG_PPC32

	p->thread.ksp_limit = (unsigned long)task_stack_page(p) +

				_ALIGN_UP(sizeof(struct thread_info), 16);



#endif

#ifdef CONFIG_HAVE_HW_BREAKPOINT

	p->thread.ptrace_bps[0] = NULL;

#endif