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arm64: reduce stack use in irq_handler

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The code for switching to irq_stack stores three pieces of information on
the stack, fp+lr, as a fake stack frame (that lets us walk back onto the
interrupted tasks stack frame), and the address of the struct pt_regs that
contains the register values from kernel entry. (which dump_backtrace()
will print in any stack trace).

To reduce this, we store fp, and the pointer to the struct pt_regs.
unwind_frame() can recognise this as the irq_stack dummy frame, (as it only
appears at the top of the irq_stack), and use the struct pt_regs values
to find the missing interrupted link-register.

Suggested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
James Morse 2015-12-15 11:21:25 +00:00 committed by Will Deacon
parent 129b985cc3
commit 971c67ce37
3 changed files with 27 additions and 15 deletions
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11
arch/arm64/include/asm/irq.h
View file

@ -25,16 +25,13 @@ DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack);
* ------------
* | | <- irq_stack_ptr
* top ------------
* | elr_el1 |
* | x19 | <- irq_stack_ptr - 0x08
* ------------
* | x29 | <- irq_stack_ptr - 0x10
* ------------
* | xzr |
* ------------
* | x19 | <- irq_stack_ptr - 0x20
* ------------
*
* where x19 holds a copy of the task stack pointer.
* where x19 holds a copy of the task stack pointer where the struct pt_regs
* from kernel_entry can be found.
*
*/
#define IRQ_STACK_PTR(cpu) ((unsigned long)per_cpu(irq_stack, cpu) + IRQ_STACK_START_SP)
@ -43,7 +40,7 @@ DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack);
* The offset from irq_stack_ptr where entry.S will store the original
* stack pointer. Used by unwind_frame() and dump_backtrace().
*/
#define IRQ_STACK_TO_TASK_STACK(ptr) *((unsigned long *)(ptr - 0x20));
#define IRQ_STACK_TO_TASK_STACK(ptr) (*((unsigned long *)((ptr) - 0x08)))
extern void set_handle_irq(void (*handle_irq)(struct pt_regs *));

12
arch/arm64/kernel/entry.S
View file

@ -178,7 +178,7 @@ alternative_endif
mrs \rd, sp_el0
.endm
.macro irq_stack_entry, dummy_lr
.macro irq_stack_entry
mov x19, sp // preserve the original sp
this_cpu_ptr irq_stack, x25, x26
@ -196,10 +196,12 @@ alternative_endif
add x26, x25, x26
mov sp, x26
/* Add a dummy stack frame */
stp x29, \dummy_lr, [sp, #-16]! // dummy stack frame
/*
* Add a dummy stack frame, this non-standard format is fixed up
* by unwind_frame()
*/
stp x29, x19, [sp, #-16]!
mov x29, sp
stp x19, xzr, [sp, #-16]!
9998:
.endm
@ -229,7 +231,7 @@ tsk .req x28 // current thread_info
.macro irq_handler
ldr_l x1, handle_arch_irq
mov x0, sp
irq_stack_entry x22
irq_stack_entry
blr x1
irq_stack_exit
.endm

19
arch/arm64/kernel/stacktrace.c
View file

@ -70,17 +70,30 @@ int notrace unwind_frame(struct stackframe *frame)
* Check whether we are going to walk through from interrupt stack
* to task stack.
* If we reach the end of the stack - and its an interrupt stack,
* read the original task stack pointer from the dummy frame.
* unpack the dummy frame to find the original elr.
*
* Check the frame->fp we read from the bottom of the irq_stack,
* and the original task stack pointer are both in current->stack.
*/
if (frame->sp == irq_stack_ptr) {
struct pt_regs *irq_args;
unsigned long orig_sp = IRQ_STACK_TO_TASK_STACK(irq_stack_ptr);
if(object_is_on_stack((void *)orig_sp) &&
object_is_on_stack((void *)frame->fp))
if (object_is_on_stack((void *)orig_sp) &&
object_is_on_stack((void *)frame->fp)) {
frame->sp = orig_sp;
/* orig_sp is the saved pt_regs, find the elr */
irq_args = (struct pt_regs *)orig_sp;
frame->pc = irq_args->pc;
} else {
/*
* This frame has a non-standard format, and we
* didn't fix it, because the data looked wrong.
* Refuse to output this frame.
*/
return -EINVAL;
}
}
return 0;