linux-kernel - Re: [PATCH 0/2] i8253: Fix PIT shutdown quirk on Hyper-V

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Date:   Fri, 2 Nov 2018 08:40:04 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "akataria@...are.com" <akataria@...are.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        vkuznets <vkuznets@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        KY Srinivasan <kys@...rosoft.com>
Subject: Re: [PATCH 0/2] i8253: Fix PIT shutdown quirk on Hyper-V

On 01/11/2018 18:30, Michael Kelley wrote:
> pit_shutdown() doesn't work on Hyper-V because of a quirk in the
> PIT emulation. This problem exists in all versions of Hyper-V and
> had not been noticed previously. When the counter register is set
> to zero, the emulated PIT continues to interrupt @18.2 HZ.
> 
> So add a test for running on Hyper-V, and use that test to skip
> setting the counter register when running on Hyper-V.
> 
> This patch replaces a previously proposed patch with a different
> approach. This new approach follows comments from Thomas Gleixner.

Did you consider using a static_key instead? You could set it in
ms_hyperv_init_platform(). This would enable you to support future
Hyper-V versions which don't require avoiding to set the count to zero.


Juergen