[PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter()

Peter Zijlstra
2020-02-21T13:50:26Z

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. We 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 NMI's 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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/traps.h | 3 -
arch/x86/kernel/cpu/mce/core.c | 16 +++++----
arch/x86/kernel/cpu/mce/p5.c | 8 ++--
arch/x86/kernel/cpu/mce/winchip.c | 8 ++--
arch/x86/kernel/traps.c | 65 +++++++-------------------------------
5 files changed, 32 insertions(+), 68 deletions(-)

--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -121,9 +121,6 @@ void smp_spurious_interrupt(struct pt_re
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,
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -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>
@@ -1221,7 +1222,7 @@ static void kill_me_maybe(struct callbac
* MCE broadcast. However some CPUs might be broken beyond repair,
* so be always careful when synchronizing with others.
*/
-void do_machine_check(struct pt_regs *regs, long error_code)
+notrace void do_machine_check(struct pt_regs *regs, long error_code)
{
DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
DECLARE_BITMAP(toclear, MAX_NR_BANKS);
@@ -1255,10 +1256,10 @@ void do_machine_check(struct pt_regs *re
*/
int lmce = 1;

- if (__mc_check_crashing_cpu(cpu))
- return;
+ nmi_enter();

- ist_enter(regs);
+ if (__mc_check_crashing_cpu(cpu))
+ goto out;

this_cpu_inc(mce_exception_count);

@@ -1347,7 +1348,7 @@ void do_machine_check(struct pt_regs *re
sync_core();

if (worst != MCE_AR_SEVERITY && !kill_it)
- goto out_ist;
+ goto out;

/* Fault was in user mode and we need to take some action */
if ((m.cs & 3) == 3) {
@@ -1363,10 +1364,11 @@ void do_machine_check(struct pt_regs *re
mce_panic("Failed kernel mode recovery", &m, msg);
}

-out_ist:
- ist_exit(regs);
+out:
+ nmi_exit();
}
EXPORT_SYMBOL_GPL(do_machine_check);
+NOKPROBE_SYMBOL(do_machine_check);

#ifndef CONFIG_MEMORY_FAILURE
int memory_failure(unsigned long pfn, int flags)
--- a/arch/x86/kernel/cpu/mce/p5.c
+++ b/arch/x86/kernel/cpu/mce/p5.c
@@ -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>
@@ -20,11 +21,11 @@
int mce_p5_enabled __read_mostly;

/* Machine check handler for Pentium class Intel CPUs: */
-static void pentium_machine_check(struct pt_regs *regs, long error_code)
+static notrace 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);
@@ -39,8 +40,9 @@ static void pentium_machine_check(struct

add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);

- ist_exit(regs);
+ nmi_exit();
}
+NOKPROBE_SYMBOL(pentium_machine_check);

/* Set up machine check reporting for processors with Intel style MCE: */
void intel_p5_mcheck_init(struct cpuinfo_x86 *c)
--- a/arch/x86/kernel/cpu/mce/winchip.c
+++ b/arch/x86/kernel/cpu/mce/winchip.c
@@ -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>
@@ -16,15 +17,16 @@
#include "internal.h"

/* Machine check handler for WinChip C6: */
-static void winchip_machine_check(struct pt_regs *regs, long error_code)
+static notrace 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();
}
+NOKPROBE_SYMBOL(winchip_machine_check);

/* Set up machine check reporting on the Winchip C6 series */
void winchip_mcheck_init(struct cpuinfo_x86 *c)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -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_disabl
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;
@@ -306,7 +273,7 @@ __visible void __noreturn handle_stack_o
* be lost. If, for some reason, we need to return to a context with modified
* regs, the shim code could be adjusted to synchronize the registers.
*/
-dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2)
+dotraplinkage notrace void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2)
{
static const char str[] = "double fault";
struct task_struct *tsk = current;
@@ -326,7 +293,7 @@ dotraplinkage void do_double_fault(struc
* 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(struc
}
#endif

- ist_enter(regs);
+ nmi_enter();
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);

tsk->thread.error_code = error_code;
@@ -413,6 +380,7 @@ dotraplinkage void do_double_fault(struc
die("double fault", regs, error_code);
panic("Machine halted.");
}
+NOKPROBE_SYMBOL(do_double_fault)
#endif

dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
@@ -549,19 +517,12 @@ dotraplinkage void do_general_protection
}
NOKPROBE_SYMBOL(do_general_protection);

-dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
+dotraplinkage notrace void do_int3(struct pt_regs *regs, long error_code)
{
if (poke_int3_handler(regs))
return;

- /*
- * Use ist_enter despite the fact that we don't use an IST stack.
- * We can be called from a kprobe in non-CONTEXT_KERNEL kernel
- * mode or even during context tracking state changes.
- *
- * This means that we can't schedule. That's okay.
- */
- ist_enter(regs);
+ nmi_enter();
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
@@ -583,7 +544,7 @@ dotraplinkage void notrace do_int3(struc
cond_local_irq_disable(regs);

exit:
- ist_exit(regs);
+ nmi_exit();
}
NOKPROBE_SYMBOL(do_int3);

@@ -680,14 +641,14 @@ static bool is_sysenter_singlestep(struc
*
* May run on IST stack.
*/
-dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
+dotraplinkage notrace void do_debug(struct pt_regs *regs, long error_code)
{
struct task_struct *tsk = current;
int user_icebp = 0;
unsigned long dr6;
int si_code;

- ist_enter(regs);
+ nmi_enter();

get_debugreg(dr6, 6);
/*
@@ -780,7 +741,7 @@ dotraplinkage void do_debug(struct pt_re
debug_stack_usage_dec();

exit:
- ist_exit(regs);
+ nmi_exit();
}
NOKPROBE_SYMBOL(do_debug);