[PATCH v4 02/27] hardirq/nmi: Allow nested nmi_enter()

Peter Zijlstra
2020-02-21T13:50:45Z

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/include/asm/hardirq.h | 4 ++--
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 ++--
kernel/printk/printk_safe.c | 6 ++++--
7 files changed, 22 insertions(+), 41 deletions(-)

--- a/arch/arm64/include/asm/hardirq.h
+++ b/arch/arm64/include/asm/hardirq.h
@@ -38,7 +38,7 @@ DECLARE_PER_CPU(struct nmi_ctx, nmi_cont

#define arch_nmi_enter() \
do { \
- if (is_kernel_in_hyp_mode()) { \
+ if (is_kernel_in_hyp_mode() && !in_nmi()) { \
struct nmi_ctx *nmi_ctx = this_cpu_ptr(&nmi_contexts); \
nmi_ctx->hcr = read_sysreg(hcr_el2); \
if (!(nmi_ctx->hcr & HCR_TGE)) { \
@@ -50,7 +50,7 @@ DECLARE_PER_CPU(struct nmi_ctx, nmi_cont

#define arch_nmi_exit() \
do { \
- if (is_kernel_in_hyp_mode()) { \
+ if (is_kernel_in_hyp_mode() && !in_nmi()) { \
struct nmi_ctx *nmi_ctx = this_cpu_ptr(&nmi_contexts); \
if (!(nmi_ctx->hcr & HCR_TGE)) \
write_sysreg(nmi_ctx->hcr, hcr_el2); \
--- a/arch/arm64/kernel/sdei.c
+++ b/arch/arm64/kernel/sdei.c
@@ -251,22 +251,12 @@ asmlinkage __kprobes notrace unsigned lo
__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;
}
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -906,17 +906,13 @@ bool arm64_is_fatal_ras_serror(struct pt

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)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -441,15 +441,9 @@ void hv_nmi_check_nonrecoverable(struct
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 @@ void system_reset_exception(struct pt_re
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
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_r
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_r
return;

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

void SMIException(struct pt_regs *regs)
--- 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(); \
trace_hardirq_enter(); \
--- 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)
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -296,12 +296,14 @@ static __printf(1, 0) int vprintk_nmi(co

void notrace printk_nmi_enter(void)
{
- this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
+ if (!in_nmi())
+ this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
}

void notrace printk_nmi_exit(void)
{
- this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
+ if (!in_nmi())
+ this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
}

/*