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: c227233ad64c (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

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 341ee4f1d91e9a53ee1f618ab91103f1a391dc64..920426d691ce7196d4b898751b7e0ee607d3b082 100644 (file)
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -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();
 }

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index dcda0afecfc5f4998266c3d557aef25ac0e50c22..3e01a6b23e75fe88b060e752aa2e66e944e236e6 100644 (file)
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -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);
 }
 
 /**