linux-kernel - Re: [PATCH 1/1] x86/hyperv: Disable hardlockup detector by default in Hyper-V guests

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Date:   Wed, 11 May 2022 14:42:37 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/hyperv: Disable hardlockup detector by default
 in Hyper-V guests

On Mon, May 09, 2022 at 08:44:23AM -0700, Michael Kelley wrote:
> In newer versions of Hyper-V, the x86/x64 PMU can be virtualized
> into guest VMs by explicitly enabling it. Linux kernels are typically
> built to automatically enable the hardlockup detector if the PMU is
> found. To prevent the possibility of false positives due to the
> vagaries of VM scheduling, disable the PMU-based hardlockup detector
> by default in a VM on Hyper-V.  The hardlockup detector can still be
> enabled by overriding the default with the nmi_watchdog=1 option on
> the kernel boot line or via sysctl at runtime.
> 
> This change mimics the approach taken with KVM guests in
> commit 692297d8f968 ("watchdog: introduce the hardlockup_detector_disable()
> function").
> 
> Linux on ARM64 does not provide a PMU-based hardlockup detector, so
> there's no corresponding disable in the Hyper-V init code on ARM64.
> 
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>

Applied to hyperv-next. Thanks.