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Date:   Wed, 11 May 2022 14:42:37 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Michael Kelley <mikelley@microsoft.com>
Cc:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
        hpa@zytor.com, linux-kernel@vger.kernel.org,
        linux-hyperv@vger.kernel.org
Subject: Re: [PATCH 1/1] x86/hyperv: Disable hardlockup detector by default
 in Hyper-V guests
Message-ID: <20220511144237.dp4gcj4zn6kof5re@liuwe-devbox-debian-v2>
References: <1652111063-6535-1-git-send-email-mikelley@microsoft.com>
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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@microsoft.com>

Applied to hyperv-next. Thanks.