linux/arch/arm/include/asm/mmu_context.h
Nicolas Pitre ec706dab29 ARM: add a vma entry for the user accessible vector page
The kernel makes the high vector page visible to user space. This page
contains (amongst others) small code segments that can be executed in
user space.  Make this page visible through ptrace and /proc/<pid>/mem
in order to let gdb perform code parsing needed for proper unwinding.

For example, the ERESTART_RESTARTBLOCK handler actually has a stack
frame -- it returns to a PC value stored on the user's stack.   To
unwind after a "sleep" system call was interrupted twice, GDB would
have to recognize this situation and understand that stack frame
layout -- which it currently cannot do.

We could fix this by hard-coding addresses in the vector page range into
GDB, but that isn't really portable as not all of those addresses are
guaranteed to remain stable across kernel releases.  And having the gdb
process make an exception for this page and get  content from its own
address space for it looks strange, and it is not future proof either.

Being located above PAGE_OFFSET, this vma cannot be deleted by
user space code.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
2010-10-01 22:35:19 -04:00

164 lines
4.4 KiB
C

/*
* arch/arm/include/asm/mmu_context.h
*
* Copyright (C) 1996 Russell King.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Changelog:
* 27-06-1996 RMK Created
*/
#ifndef __ASM_ARM_MMU_CONTEXT_H
#define __ASM_ARM_MMU_CONTEXT_H
#include <linux/compiler.h>
#include <linux/sched.h>
#include <asm/cacheflush.h>
#include <asm/cachetype.h>
#include <asm/proc-fns.h>
void __check_kvm_seq(struct mm_struct *mm);
#ifdef CONFIG_CPU_HAS_ASID
/*
* On ARMv6, we have the following structure in the Context ID:
*
* 31 7 0
* +-------------------------+-----------+
* | process ID | ASID |
* +-------------------------+-----------+
* | context ID |
* +-------------------------------------+
*
* The ASID is used to tag entries in the CPU caches and TLBs.
* The context ID is used by debuggers and trace logic, and
* should be unique within all running processes.
*/
#define ASID_BITS 8
#define ASID_MASK ((~0) << ASID_BITS)
#define ASID_FIRST_VERSION (1 << ASID_BITS)
extern unsigned int cpu_last_asid;
#ifdef CONFIG_SMP
DECLARE_PER_CPU(struct mm_struct *, current_mm);
#endif
void __init_new_context(struct task_struct *tsk, struct mm_struct *mm);
void __new_context(struct mm_struct *mm);
static inline void check_context(struct mm_struct *mm)
{
/*
* This code is executed with interrupts enabled. Therefore,
* mm->context.id cannot be updated to the latest ASID version
* on a different CPU (and condition below not triggered)
* without first getting an IPI to reset the context. The
* alternative is to take a read_lock on mm->context.id_lock
* (after changing its type to rwlock_t).
*/
if (unlikely((mm->context.id ^ cpu_last_asid) >> ASID_BITS))
__new_context(mm);
if (unlikely(mm->context.kvm_seq != init_mm.context.kvm_seq))
__check_kvm_seq(mm);
}
#define init_new_context(tsk,mm) (__init_new_context(tsk,mm),0)
#else
static inline void check_context(struct mm_struct *mm)
{
#ifdef CONFIG_MMU
if (unlikely(mm->context.kvm_seq != init_mm.context.kvm_seq))
__check_kvm_seq(mm);
#endif
}
#define init_new_context(tsk,mm) 0
#endif
#define destroy_context(mm) do { } while(0)
/*
* This is called when "tsk" is about to enter lazy TLB mode.
*
* mm: describes the currently active mm context
* tsk: task which is entering lazy tlb
* cpu: cpu number which is entering lazy tlb
*
* tsk->mm will be NULL
*/
static inline void
enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
}
/*
* This is the actual mm switch as far as the scheduler
* is concerned. No registers are touched. We avoid
* calling the CPU specific function when the mm hasn't
* actually changed.
*/
static inline void
switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk)
{
#ifdef CONFIG_MMU
unsigned int cpu = smp_processor_id();
#ifdef CONFIG_SMP
/* check for possible thread migration */
if (!cpumask_empty(mm_cpumask(next)) &&
!cpumask_test_cpu(cpu, mm_cpumask(next)))
__flush_icache_all();
#endif
if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next) {
#ifdef CONFIG_SMP
struct mm_struct **crt_mm = &per_cpu(current_mm, cpu);
*crt_mm = next;
#endif
check_context(next);
cpu_switch_mm(next->pgd, next);
if (cache_is_vivt())
cpumask_clear_cpu(cpu, mm_cpumask(prev));
}
#endif
}
#define deactivate_mm(tsk,mm) do { } while (0)
#define activate_mm(prev,next) switch_mm(prev, next, NULL)
/*
* We are inserting a "fake" vma for the user-accessible vector page so
* gdb and friends can get to it through ptrace and /proc/<pid>/mem.
* But we also want to remove it before the generic code gets to see it
* during process exit or the unmapping of it would cause total havoc.
* (the macro is used as remove_vma() is static to mm/mmap.c)
*/
#define arch_exit_mmap(mm) \
do { \
struct vm_area_struct *high_vma = find_vma(mm, 0xffff0000); \
if (high_vma) { \
BUG_ON(high_vma->vm_next); /* it should be last */ \
if (high_vma->vm_prev) \
high_vma->vm_prev->vm_next = NULL; \
else \
mm->mmap = NULL; \
rb_erase(&high_vma->vm_rb, &mm->mm_rb); \
mm->mmap_cache = NULL; \
mm->map_count--; \
remove_vma(high_vma); \
} \
} while (0)
static inline void arch_dup_mmap(struct mm_struct *oldmm,
struct mm_struct *mm)
{
}
#endif