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x86: Replace ist_enter() with nmi_enter()

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A few exceptions (like #DB and #BP) can happen at any location in the code,
this then means that tracers should treat events from these exceptions as
NMI-like. The interrupted context could be holding locks with interrupts
disabled for instance.

Similarly, #MC is an actual NMI-like exception.

All of them use ist_enter() which only concerns itself with RCU, but does
not do any of the other setup that NMIs need. This means things like:

	printk()
	  raw_spin_lock_irq(&logbuf_lock);
	  <#DB/#BP/#MC>
	     printk()
	       raw_spin_lock_irq(&logbuf_lock);

are entirely possible (well, not really since printk tries hard to
play nice, but the concept stands).

So replace ist_enter() with nmi_enter(). Also observe that any nmi_enter()
caller must be both notrace and NOKPROBE, or in the noinstr text section.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/20200505134101.525508608@linutronix.de
This commit is contained in:
Peter Zijlstra 2020-02-19 09:46:43 +01:00 committed by Thomas Gleixner
parent 5567d11c21
commit 0d00449c7a
5 changed files with 24 additions and 65 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
arch/x86/include/asm/traps.h
View file

@ -118,9 +118,6 @@ void smp_spurious_interrupt(struct pt_regs *regs);
void smp_error_interrupt(struct pt_regs *regs);
asmlinkage void smp_irq_move_cleanup_interrupt(void);
extern void ist_enter(struct pt_regs *regs);
extern void ist_exit(struct pt_regs *regs);
#ifdef CONFIG_VMAP_STACK
void __noreturn handle_stack_overflow(const char *message,
struct pt_regs *regs,

5
arch/x86/kernel/cpu/mce/core.c
View file

@ -43,6 +43,7 @@
#include <linux/jump_label.h>
#include <linux/set_memory.h>
#include <linux/task_work.h>
#include <linux/hardirq.h>
#include <asm/intel-family.h>
#include <asm/processor.h>
@ -1266,7 +1267,7 @@ void noinstr do_machine_check(struct pt_regs *regs, long error_code)
if (__mc_check_crashing_cpu(cpu))
return;
ist_enter(regs);
nmi_enter();
this_cpu_inc(mce_exception_count);
@ -1374,7 +1375,7 @@ void noinstr do_machine_check(struct pt_regs *regs, long error_code)
}
out_ist:
ist_exit(regs);
nmi_exit();
}
EXPORT_SYMBOL_GPL(do_machine_check);

5
arch/x86/kernel/cpu/mce/p5.c
View file

@ -7,6 +7,7 @@
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/smp.h>
#include <linux/hardirq.h>
#include <asm/processor.h>
#include <asm/traps.h>
@ -24,7 +25,7 @@ static void pentium_machine_check(struct pt_regs *regs, long error_code)
{
u32 loaddr, hi, lotype;
ist_enter(regs);
nmi_enter();
rdmsr(MSR_IA32_P5_MC_ADDR, loaddr, hi);
rdmsr(MSR_IA32_P5_MC_TYPE, lotype, hi);
@ -39,7 +40,7 @@ static void pentium_machine_check(struct pt_regs *regs, long error_code)
add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
ist_exit(regs);
nmi_exit();
}
/* Set up machine check reporting for processors with Intel style MCE: */

5
arch/x86/kernel/cpu/mce/winchip.c
View file

@ -6,6 +6,7 @@
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/hardirq.h>
#include <asm/processor.h>
#include <asm/traps.h>
@ -18,12 +19,12 @@
/* Machine check handler for WinChip C6: */
static void winchip_machine_check(struct pt_regs *regs, long error_code)
{
ist_enter(regs);
nmi_enter();
pr_emerg("CPU0: Machine Check Exception.\n");
add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
ist_exit(regs);
nmi_exit();
}
/* Set up machine check reporting on the Winchip C6 series */

71
arch/x86/kernel/traps.c
View file

@ -37,10 +37,12 @@
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/io.h>
#include <linux/hardirq.h>
#include <linux/atomic.h>
#include <asm/stacktrace.h>
#include <asm/processor.h>
#include <asm/debugreg.h>
#include <linux/atomic.h>
#include <asm/text-patching.h>
#include <asm/ftrace.h>
#include <asm/traps.h>
@ -82,41 +84,6 @@ static inline void cond_local_irq_disable(struct pt_regs *regs)
local_irq_disable();
}
/*
* In IST context, we explicitly disable preemption. This serves two
* purposes: it makes it much less likely that we would accidentally
* schedule in IST context and it will force a warning if we somehow
* manage to schedule by accident.
*/
void ist_enter(struct pt_regs *regs)
{
if (user_mode(regs)) {
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
} 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();
}
preempt_disable();
/* This code is a bit fragile. Test it. */
RCU_LOCKDEP_WARN(!rcu_is_watching(), "ist_enter didn't work");
}
NOKPROBE_SYMBOL(ist_enter);
void ist_exit(struct pt_regs *regs)
{
preempt_enable_no_resched();
if (!user_mode(regs))
rcu_nmi_exit();
}
int is_valid_bugaddr(unsigned long addr)
{
unsigned short ud;
@ -326,7 +293,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign
* The net result is that our #GP handler will think that we
* entered from usermode with the bad user context.
*
* No need for ist_enter here because we don't use RCU.
* No need for nmi_enter() here because we don't use RCU.
*/
if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY &&
regs->cs == __KERNEL_CS &&
@ -361,7 +328,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign
}
#endif
ist_enter(regs);
nmi_enter();
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
tsk->thread.error_code = error_code;
@ -555,19 +522,13 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
return;
/*
* Unlike any other non-IST entry, we can be called from a kprobe in
* non-CONTEXT_KERNEL kernel mode or even during context tracking
* state changes. Make sure that we wake up RCU even if we're coming
* from kernel code.
*
* This means that we can't schedule even if we came from a
* preemptible kernel context. That's okay.
* Unlike any other non-IST entry, we can be called from pretty much
* any location in the kernel through kprobes -- text_poke() will most
* likely be handled by poke_int3_handler() above. This means this
* handler is effectively NMI-like.
*/
if (!user_mode(regs)) {
rcu_nmi_enter();
preempt_disable();
}
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
if (!user_mode(regs))
nmi_enter();
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
@ -589,10 +550,8 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
cond_local_irq_disable(regs);
exit:
if (!user_mode(regs)) {
preempt_enable_no_resched();
rcu_nmi_exit();
}
if (!user_mode(regs))
nmi_exit();
}
NOKPROBE_SYMBOL(do_int3);
@ -696,7 +655,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
unsigned long dr6;
int si_code;
ist_enter(regs);
nmi_enter();
get_debugreg(dr6, 6);
/*
@ -789,7 +748,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
debug_stack_usage_dec();
exit:
ist_exit(regs);
nmi_exit();
}
NOKPROBE_SYMBOL(do_debug);