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From: Thomas Gleixner <tglx@linutronix.de>
To: Juergen Gross <jgross@suse.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
	sthemmin@microsoft.com, mikelley@microsoft.com,
	kys@microsoft.com, haiyangz@microsoft.com,
	yi.y.sun@linux.intel.com, hpa@zytor.com
Subject: Re: [tip:x86/hyperv] x86/hyperv: Enable PV qspinlock for Hyper-V
Date: Tue, 2 Oct 2018 14:13:14 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1810021412060.12704@nanos.tec.linutronix.de> (raw)
In-Reply-To: <0005fc50-4415-87a0-1954-fb15a1f8bd0b@suse.com>

On Tue, 2 Oct 2018, Juergen Gross wrote:

> Sorry for noticing this only now, but I have been fighting with
> Xen PV qspinlocks last weekend:
> 
> > +	/*
> > +	 * Read HV_X64_MSR_GUEST_IDLE MSR can trigger the guest's
> > +	 * transition to the idle power state which can be exited
> > +	 * by an IPI even if IF flag is disabled.
> > +	 */
> 
> What if interrupts are enabled? Won't a kick happening here just
> interrupt and then the following rdmsr result in a hang?
> 
> I believe the correct way would be to:
> 
> - disable interrupts before above READ_ONCE() and restore them
>   after the rdmsrl()
> 
> - return early if in_nmi()
> 
> similar as the kvm specific variant is doing it.

Interesting question. I zapped the last commit for now until this is
clarified.

Thanks,

	tglx

  reply	other threads:[~2018-10-02 12:13 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-27  6:01 [PATCH v3 0/2] Enable PV qspinlock for Hyper-V Yi Sun
2018-09-27  6:01 ` [PATCH v3 1/2] X86/Hyper-V: Add Guest IDLE MSR support Yi Sun
2018-10-02 11:27   ` [tip:x86/hyperv] x86/hyperv: Add GUEST_IDLE_MSR support tip-bot for Yi Sun
2018-10-09 12:27   ` [tip:x86/paravirt] " tip-bot for Yi Sun
2018-09-27  6:01 ` [PATCH v3 2/2] locking/pvqspinlock, hv: Enable PV qspinlock for Hyper-V Yi Sun
2018-09-28 22:09   ` Michael Kelley (EOSG)
2018-10-02 11:28   ` [tip:x86/hyperv] x86/hyperv: " tip-bot for Yi Sun
2018-10-02 11:38     ` Juergen Gross
2018-10-02 12:13       ` Thomas Gleixner [this message]
2018-10-08  8:12       ` Yi Sun
2018-10-08  8:29 [PATCH v4 2/2] locking/pvqspinlock, hv: " Yi Sun
2018-10-09  9:30 ` [tip:x86/hyperv] x86/hyperv: " tip-bot for Yi Sun

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