From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05E0BC2BB3F for ; Wed, 15 Nov 2023 15:53:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232525AbjKOPxi (ORCPT ); Wed, 15 Nov 2023 10:53:38 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39342 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231605AbjKOPxN (ORCPT ); Wed, 15 Nov 2023 10:53:13 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2746C1984 for ; Wed, 15 Nov 2023 07:52:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Ohw8B+zfYq83PiKh9y615T9FB+14QEtb0yQj55L35vo=; b=kbDZgjCN23Mf9HFPPOewICpcar nLURtKdc1k6B7eeBATeTKp9Y+LOA7fC3C9voX6MdqlD+W9VPemJ64b9hP8uP8Wa/3j7PRiXDwIxRK yoKrVsk8QtAWkSGGi/+kL1C+Pgd/OQ/sZXiI7z2UoMcP3q+pMMOlRVN1me7w2yIoLnOepceCcSqip yitP+LxYnYpPKgA/MyxeC/88Mqx9N30WuTXOxY/ukZYqKEbkdquXlHFh2AP6pC2mLYiwCcY2AiiLC YpEG8nBj6zQ8Mh5EVIYtvSWZMx/IWAWULNWIkny1IMirGPrK3g2ervG7ZDvdOrKDvWg5Zfkp4MQZt Dhb9TSCA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r3IBs-0047qU-2V; Wed, 15 Nov 2023 15:52:32 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 709B1300427; Wed, 15 Nov 2023 16:52:32 +0100 (CET) Date: Wed, 15 Nov 2023 16:52:32 +0100 From: Peter Zijlstra To: Frederic Weisbecker Cc: LKML , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "Rafael J . Wysocki" Subject: Re: [PATCH 2/4] x86: Fix CPUIDLE_FLAG_IRQ_ENABLE leaking timer reprogram Message-ID: <20231115155232.GD8262@noisy.programming.kicks-ass.net> References: <20231115151325.6262-1-frederic@kernel.org> <20231115151325.6262-3-frederic@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231115151325.6262-3-frederic@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 15, 2023 at 10:13:23AM -0500, Frederic Weisbecker wrote: > From: Peter Zijlstra > > 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) > Not-yet-signed-off-by: Peter Zijlstra Feel free to change to normal SOB, I'm assuming it actually compiles and works by now :-) > Acked-by: Rafael J. Wysocki > Signed-off-by: Frederic Weisbecker > --- > 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 341ee4f1d91e..920426d691ce 100644 > --- 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 *)¤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 dcda0afecfc5..3e01a6b23e75 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) > __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); > } > > /** > -- > 2.42.1 >