diff options
Diffstat (limited to 'arch/x86/kernel/traps.c')
| -rw-r--r-- | arch/x86/kernel/traps.c | 108 |
1 files changed, 84 insertions, 24 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 88900e288021..7176f84f95a4 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -108,6 +108,77 @@ static inline void preempt_conditional_cli(struct pt_regs *regs) preempt_count_dec(); } +enum ctx_state ist_enter(struct pt_regs *regs) +{ + /* + * We are atomic because we're on the IST stack (or we're on x86_32, + * in which case we still shouldn't schedule. + */ + preempt_count_add(HARDIRQ_OFFSET); + + if (user_mode_vm(regs)) { + /* Other than that, we're just an exception. */ + return exception_enter(); + } else { + /* + * We might have interrupted pretty much anything. In + * fact, if we're a machine check, we can even interrupt + * NMI processing. We don't want in_nmi() to return true, + * but we need to notify RCU. + */ + rcu_nmi_enter(); + return IN_KERNEL; /* the value is irrelevant. */ + } +} + +void ist_exit(struct pt_regs *regs, enum ctx_state prev_state) +{ + preempt_count_sub(HARDIRQ_OFFSET); + + if (user_mode_vm(regs)) + return exception_exit(prev_state); + else + rcu_nmi_exit(); +} + +/** + * ist_begin_non_atomic() - begin a non-atomic section in an IST exception + * @regs: regs passed to the IST exception handler + * + * IST exception handlers normally cannot schedule. As a special + * exception, if the exception interrupted userspace code (i.e. + * user_mode_vm(regs) would return true) and the exception was not + * a double fault, it can be safe to schedule. ist_begin_non_atomic() + * begins a non-atomic section within an ist_enter()/ist_exit() region. + * Callers are responsible for enabling interrupts themselves inside + * the non-atomic section, and callers must call is_end_non_atomic() + * before ist_exit(). + */ +void ist_begin_non_atomic(struct pt_regs *regs) +{ + BUG_ON(!user_mode_vm(regs)); + + /* + * Sanity check: we need to be on the normal thread stack. This + * will catch asm bugs and any attempt to use ist_preempt_enable + * from double_fault. + */ + BUG_ON(((current_stack_pointer() ^ this_cpu_read_stable(kernel_stack)) + & ~(THREAD_SIZE - 1)) != 0); + + preempt_count_sub(HARDIRQ_OFFSET); +} + +/** + * ist_end_non_atomic() - begin a non-atomic section in an IST exception + * + * Ends a non-atomic section started with ist_begin_non_atomic(). + */ +void ist_end_non_atomic(void) +{ + preempt_count_add(HARDIRQ_OFFSET); +} + static nokprobe_inline int do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str, struct pt_regs *regs, long error_code) @@ -251,6 +322,8 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) * end up promoting it to a doublefault. In that case, modify * the stack to make it look like we just entered the #GP * handler from user space, similar to bad_iret. + * + * No need for ist_enter here because we don't use RCU. */ if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY && regs->cs == __KERNEL_CS && @@ -263,12 +336,12 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) normal_regs->orig_ax = 0; /* Missing (lost) #GP error code */ regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&normal_regs->orig_ax; + return; } #endif - exception_enter(); - /* Return not checked because double check cannot be ignored */ + ist_enter(regs); /* Discard prev_state because we won't return. */ notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV); tsk->thread.error_code = error_code; @@ -434,7 +507,7 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) if (poke_int3_handler(regs)) return; - prev_state = exception_enter(); + prev_state = ist_enter(regs); #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, SIGTRAP) == NOTIFY_STOP) @@ -460,33 +533,20 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) preempt_conditional_cli(regs); debug_stack_usage_dec(); exit: - exception_exit(prev_state); + ist_exit(regs, prev_state); } NOKPROBE_SYMBOL(do_int3); #ifdef CONFIG_X86_64 /* - * Help handler running on IST stack to switch back to user stack - * for scheduling or signal handling. The actual stack switch is done in - * entry.S + * Help handler running on IST stack to switch off the IST stack if the + * interrupted code was in user mode. The actual stack switch is done in + * entry_64.S */ asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs) { - struct pt_regs *regs = eregs; - /* Did already sync */ - if (eregs == (struct pt_regs *)eregs->sp) - ; - /* Exception from user space */ - else if (user_mode(eregs)) - regs = task_pt_regs(current); - /* - * Exception from kernel and interrupts are enabled. Move to - * kernel process stack. - */ - else if (eregs->flags & X86_EFLAGS_IF) - regs = (struct pt_regs *)(eregs->sp -= sizeof(struct pt_regs)); - if (eregs != regs) - *regs = *eregs; + struct pt_regs *regs = task_pt_regs(current); + *regs = *eregs; return regs; } NOKPROBE_SYMBOL(sync_regs); @@ -554,7 +614,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) unsigned long dr6; int si_code; - prev_state = exception_enter(); + prev_state = ist_enter(regs); get_debugreg(dr6, 6); @@ -629,7 +689,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) debug_stack_usage_dec(); exit: - exception_exit(prev_state); + ist_exit(regs, prev_state); } NOKPROBE_SYMBOL(do_debug); |