Patch "x86: Fix CPUIDLE_FLAG_IRQ_ENABLE leaking timer reprogram" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86: Fix CPUIDLE_FLAG_IRQ_ENABLE leaking timer reprogram

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-fix-cpuidle_flag_irq_enable-leaking-timer-reprog.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 98cc5472ca97b58dfc33c3c1bb56df3ed91597fd
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:   Wed Nov 15 10:13:23 2023 -0500

    x86: Fix CPUIDLE_FLAG_IRQ_ENABLE leaking timer reprogram
    
    [ Upstream commit edc8fc01f608108b0b7580cb2c29dfb5135e5f0e ]
    
    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@xxxxxxxxxxxxx>
    Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
    Link: https://lkml.kernel.org/r/20231115151325.6262-3-frederic@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 778df05f8539..bae83810505b 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -115,8 +115,15 @@ 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 ea5a6a14c553..45500d2d5b4b 100644
--- 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)
 		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
 
-	ret = __intel_idle(dev, drv, index);
+	ret = __intel_idle(dev, drv, index, true);
 
 	if (smt_active)
 		native_wrmsrl(MSR_IA32_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);
 }
 
 /**