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From: Thomas Gleixner <tglx@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Binbin Wu <binbin.wu@linux.intel.com>, "Verma, Vishal L"
 <vishal.l.verma@intel.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
 "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>, "Wu, Binbin"
 <binbin.wu@intel.com>, "x86@kernel.org" <x86@kernel.org>
Subject: Re: CPU Lockups in KVM with deferred hrtimer rearming
In-Reply-To: <20260421113212.GI3126523@noisy.programming.kicks-ass.net>
References: <70cd3e97fbb796e2eb2ff8cd4b7614ada05a5f24.camel@intel.com>
 <87mryxekxy.ffs@tglx>
 <770ae152-c3fd-4068-8462-23064de02238@linux.intel.com>
 <87eck8daot.ffs@tglx>
 <20260421111858.GH3126523@noisy.programming.kicks-ass.net>
 <20260421113212.GI3126523@noisy.programming.kicks-ass.net>
Date: Tue, 21 Apr 2026 18:30:43 +0200
Message-ID: <87jyu0b7ik.ffs@tglx>
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On Tue, Apr 21 2026 at 13:32, Peter Zijlstra wrote:
> On Tue, Apr 21, 2026 at 01:18:58PM +0200, Peter Zijlstra wrote:
>> >  		/*
>> > +		 * This is sadly required due to KVM, which invokes regular
>> > +		 * interrupt handlers with interrupt disabled state in @regs.
>> > +		 */
>> > +		instrumentation_begin();
>> > +		hrtimer_rearm_deferred();
>> > +		instrumentation_end();
>> > +
>> > +		/*
>> >  		 * IRQ flags state is correct already. Just tell RCU if it
>> >  		 * was not watching on entry.
>> >  		 */
>
> Ohhh, wait. What happens if you take a page-fault from NMI context? Does
> this then not result in trying to program the timer from NMI context?

Uuuurgh, yes.