6.6-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ 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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/mwait.h | 11 +++++++++-- drivers/idle/intel_idle.c | 19 +++++++------------ 2 files changed, 16 insertions(+), 14 deletions(-)
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 *)¤t_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); }
/**