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x86: Fix CPUIDLE_FLAG_IRQ_ENABLE leaking timer reprogram 

intel_idle_irq() re-enables IRQs very early. As a result, an interrupt
may fire before mwait() is eventually called. If such an interrupt queues
a timer, it may go unnoticed until mwait returns and the idle loop
handles the tick re-evaluation. And monitoring TIF_NEED_RESCHED doesn't
help because a local timer enqueue doesn't set that flag.

The issue is mitigated by the fact that this idle handler is only invoked
for shallow C-states when, presumably, the next tick is supposed to be
close enough. There may still be rare cases though when the next tick
is far away and the selected C-state is shallow, resulting in a timer
getting ignored for a while.

Fix this with using sti_mwait() whose IRQ-reenablement only triggers
upon calling mwait(), dealing with the race while keeping the interrupt
latency within acceptable bounds.

Fixes: c227233ad6 (intel_idle: enable interrupts before C1 on Xeons)
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lkml.kernel.org/r/20231115151325.6262-3-frederic@kernel.org
This commit is contained in:
Peter Zijlstra 2023-11-15 10:13:23 -05:00
parent 7d09a052a3
commit edc8fc01f6
2 changed files with 16 additions and 14 deletions
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11
arch/x86/include/asm/mwait.h
View File

@ -124,8 +124,15 @@ static __always_inline void mwait_idle_with_hints(unsigned long eax, unsigned lo
}
__monitor((void *)&current_thread_info()->flags, 0, 0);
if (!need_resched())
__mwait(eax, ecx);
if (!need_resched()) {
if (ecx & 1) {
__mwait(eax, ecx);
} else {
__sti_mwait(eax, ecx);
raw_local_irq_disable();
}
}
}
current_clr_polling();
}

19
drivers/idle/intel_idle.c
View File

@ -131,11 +131,12 @@ static unsigned int mwait_substates __initdata;
#define MWAIT2flg(eax) ((eax & 0xFF) << 24)
static __always_inline int __intel_idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
struct cpuidle_driver *drv,
int index, bool irqoff)
{
struct cpuidle_state *state = &drv->states[index];
unsigned long eax = flg2MWAIT(state->flags);
unsigned long ecx = 1; /* break on interrupt flag */
unsigned long ecx = 1*irqoff; /* break on interrupt flag */
mwait_idle_with_hints(eax, ecx);
@ -159,19 +160,13 @@ static __always_inline int __intel_idle(struct cpuidle_device *dev,
static __cpuidle int intel_idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
{
return __intel_idle(dev, drv, index);
return __intel_idle(dev, drv, index, true);
}
static __cpuidle int intel_idle_irq(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
{
int ret;
raw_local_irq_enable();
ret = __intel_idle(dev, drv, index);
raw_local_irq_disable();
return ret;
return __intel_idle(dev, drv, index, false);
}
static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
@ -184,7 +179,7 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
if (smt_active)
__update_spec_ctrl(0);
ret = __intel_idle(dev, drv, index);
ret = __intel_idle(dev, drv, index, true);
if (smt_active)
__update_spec_ctrl(spec_ctrl);
@ -196,7 +191,7 @@ static __cpuidle int intel_idle_xstate(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
{
fpu_idle_fpregs();
return __intel_idle(dev, drv, index);
return __intel_idle(dev, drv, index, true);
}
/**