[tip: core/rcu] hardirq/nmi: Allow nested nmi_enter()

tip-bot2 for Peter Zijlstra
2020-05-19T19:53:17Z

The following commit has been merged into the core/rcu branch of tip:

Commit-ID: 69ea03b56ed2c7189ccd0b5910ad39f3cad1df21
Gitweb: https://git.kernel.org/tip/69ea03b56ed2c7189ccd0b5910ad39f3cad1df21
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 19 Feb 2020 09:46:47 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 19 May 2020 15:51:17 +02:00

hardirq/nmi: Allow nested nmi_enter()

Since there are already a number of sites (ARM64, PowerPC) that effectively
nest nmi_enter(), make the primitive support this before adding even more.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Marc Zyngier <maz@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lkml.kernel.org/r/20200505134100.864179229@linutronix.de

---
arch/arm64/kernel/sdei.c | 14 ++------------
arch/arm64/kernel/traps.c | 8 ++------
arch/powerpc/kernel/traps.c | 22 ++++++----------------
include/linux/hardirq.h | 5 ++++-
include/linux/preempt.h | 4 ++--
5 files changed, 16 insertions(+), 37 deletions(-)

diff --git a/arch/arm64/kernel/sdei.c b/arch/arm64/kernel/sdei.c
index d6259da..e396e69 100644
--- a/arch/arm64/kernel/sdei.c
+++ b/arch/arm64/kernel/sdei.c
@@ -251,22 +251,12 @@ asmlinkage __kprobes notrace unsigned long
__sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
{
unsigned long ret;
- bool do_nmi_exit = false;

- /*
- * nmi_enter() deals with printk() re-entrance and use of RCU when
- * RCU believed this CPU was idle. Because critical events can
- * interrupt normal events, we may already be in_nmi().
- */
- if (!in_nmi()) {
- nmi_enter();
- do_nmi_exit = true;
- }
+ nmi_enter();

ret = _sdei_handler(regs, arg);

- if (do_nmi_exit)
- nmi_exit();
+ nmi_exit();

return ret;
}
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index cf402be..c728f16 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -906,17 +906,13 @@ bool arm64_is_fatal_ras_serror(struct pt_regs *regs, unsigned int esr)

asmlinkage void do_serror(struct pt_regs *regs, unsigned int esr)
{
- const bool was_in_nmi = in_nmi();
-
- if (!was_in_nmi)
- nmi_enter();
+ nmi_enter();

/* non-RAS errors are not containable */
if (!arm64_is_ras_serror(esr) || arm64_is_fatal_ras_serror(regs, esr))
arm64_serror_panic(regs, esr);

- if (!was_in_nmi)
- nmi_exit();
+ nmi_exit();
}

asmlinkage void enter_from_user_mode(void)
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 3fca222..b44dd75 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -441,15 +441,9 @@ nonrecoverable:
void system_reset_exception(struct pt_regs *regs)
{
unsigned long hsrr0, hsrr1;
- bool nested = in_nmi();
bool saved_hsrrs = false;

- /*
- * Avoid crashes in case of nested NMI exceptions. Recoverability
- * is determined by RI and in_nmi
- */
- if (!nested)
- nmi_enter();
+ nmi_enter();

/*
* System reset can interrupt code where HSRRs are live and MSR[RI]=1.
@@ -521,8 +515,7 @@ out:
mtspr(SPRN_HSRR1, hsrr1);
}

- if (!nested)
- nmi_exit();
+ nmi_exit();

/* What should we do here? We could issue a shutdown or hard reset. */
}
@@ -823,9 +816,8 @@ int machine_check_generic(struct pt_regs *regs)
void machine_check_exception(struct pt_regs *regs)
{
int recover = 0;
- bool nested = in_nmi();
- if (!nested)
- nmi_enter();
+
+ nmi_enter();

__this_cpu_inc(irq_stat.mce_exceptions);

@@ -851,8 +843,7 @@ void machine_check_exception(struct pt_regs *regs)
if (check_io_access(regs))
goto bail;

- if (!nested)
- nmi_exit();
+ nmi_exit();

die("Machine check", regs, SIGBUS);

@@ -863,8 +854,7 @@ void machine_check_exception(struct pt_regs *regs)
return;

bail:
- if (!nested)
- nmi_exit();
+ nmi_exit();
}

void SMIException(struct pt_regs *regs)
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 7c8b82f..a043ad8 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -65,13 +65,16 @@ extern void irq_exit(void);
#define arch_nmi_exit() do { } while (0)
#endif

+/*
+ * nmi_enter() can nest up to 15 times; see NMI_BITS.
+ */
#define nmi_enter() \
do { \
arch_nmi_enter(); \
printk_nmi_enter(); \
lockdep_off(); \
ftrace_nmi_enter(); \
- BUG_ON(in_nmi()); \
+ BUG_ON(in_nmi() == NMI_MASK); \
preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
rcu_nmi_enter(); \
lockdep_hardirq_enter(); \
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index bc3f1ae..7d9c1c0 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -26,13 +26,13 @@
* PREEMPT_MASK: 0x000000ff
* SOFTIRQ_MASK: 0x0000ff00
* HARDIRQ_MASK: 0x000f0000
- * NMI_MASK: 0x00100000
+ * NMI_MASK: 0x00f00000
* PREEMPT_NEED_RESCHED: 0x80000000
*/
#define PREEMPT_BITS 8
#define SOFTIRQ_BITS 8
#define HARDIRQ_BITS 4
-#define NMI_BITS 1
+#define NMI_BITS 4

#define PREEMPT_SHIFT 0
#define SOFTIRQ_SHIFT (PREEMPT_SHIFT + PREEMPT_BITS)