linux-kernel - Re: [PATCH v2 05/19] KVM: Rename and move CPUHP_AP_KVM

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Date:   Thu, 1 Sep 2022 13:59:49 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     <isaku.yamahata@...el.com>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <isaku.yamahata@...il.com>, Paolo Bonzini <pbonzini@...hat.com>,
        "Sean Christopherson" <seanjc@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        "Will Deacon" <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 05/19] KVM: Rename and move CPUHP_AP_KVM_STARTING to
 ONLINE section

On Tue, Aug 30, 2022 at 05:01:20AM -0700, isaku.yamahata@...el.com wrote:
>From: Chao Gao <chao.gao@...el.com>
>
>The CPU STARTING section doesn't allow callbacks to fail. Move KVM's
>hotplug callback to ONLINE section so that it can abort onlining a CPU in
>certain cases to avoid potentially breaking VMs running on existing CPUs.
>For example, when kvm fails to enable hardware virtualization on the
>hotplugged CPU.
>
>Place KVM's hotplug state before CPUHP_AP_SCHED_WAIT_EMPTY as it ensures
>when offlining a CPU, all user tasks and non-pinned kernel tasks have left
>the CPU, i.e. there cannot be a vCPU task around. So, it is safe for KVM's
>CPU offline callback to disable hardware virtualization at that point.
>Likewise, KVM's online callback can enable hardware virtualization before
>any vCPU task gets a chance to run on hotplugged CPUs.
>
>KVM's CPU hotplug callbacks are renamed as well.
>
>Suggested-by: Thomas Gleixner <tglx@...utronix.de>
>Signed-off-by: Chao Gao <chao.gao@...el.com>
>Link: https://lore.kernel.org/r/20220216031528.92558-6-chao.gao@intel.com

Note that Sean gave his Reviewed-by for KVM changes.

https://lore.kernel.org/all/Yg%2FmxKrB5ZoRBIG+@google.com/